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At least 199 records · Page 11Linked to original sources
PubMed1989

Defective gene in lactic acidosis: abnormal pyruvate dehydrogenase E1 alpha-subunit caused by a frame shift.

A patient with lactic acidosis showed a lowered pyruvate dehydrogenase E1 activity and fatigued on slight exercise. The cDNA encoding the pyruvate dehydrogenase E1 alpha-subunit from his lymphocytes, transformed by infection of Epstein-Barr virus, was cloned and sequenced. The nucleotide sequence determination revealed that the gene had a deletion of four nucleotides at the second codon upstream from the termination codon. This deletion would lead to a reading-frame shift and make a new termination codon at the 33d codon downstream from the "normal" termination codon. An S1 nuclease-protection experiment confirmed the presence of mRNA with its deletion in the patient. Amplification, by the polymerase chain reaction method, of the genomic-DNA region from his peripheral blood cells showed that the deletion was localized in an exon and that it was not caused by an abnormal splicing at the intron/exon junction. This is the first report on cloning a defective gene of the pyruvate dehydrogenase complex.

Acidosis, Lactic↗
PubMed1987

Spiroplasma virus 4: nucleotide sequence of the viral DNA, regulatory signals, and proposed genome organization.

The replicative form (RF) of spiroplasma virus 4 (SpV4) has been cloned in Escherichia coli, and the cloned RF has been shown to be infectious by transfection (M. C. Pascarel-Devilder, J. Renaudin, and J.-M. Bové, Virology 151:390-393, 1986). The cloned SpV4 RF was randomly subcloned and was fully sequenced by the dideoxy chain termination technique, using the M13 cloning and sequencing system. The nucleotide sequence of the SpV4 genome contains 4,421 nucleotides with a G+C content of 32 mol%. The triplet TGA is not a termination codon but, as in Mycoplasma capricolum (F. Yamao, A. Muto, Y. Kawauchi, M. Iwami, S. Iwagani, Y. Azumi, and S. Osawa, Proc. Natl. Acad. Sci. USA 82:2306-2309, 1985), probably codes for tryptophan. With these assumptions, nine open reading frames (ORFs) were identified. All nine are characterized by an ATG or GTG initiation codon, one or several termination codons, and a Shine-Dalgarno sequence upstream of the initiation codon. The nine ORFs are distributed in all three reading frames. One of the ORFs (ORF1) corresponds to the 60,000-dalton capsid protein gene. Analysis of codon usage showed that T- and A-terminated codons are preferably used, reflecting the low G+C content (32 mol%) of the SpV4 genome. The viral DNA contains two G+C-rich inverted repeat sequences. One could be involved in transcription termination and the other in initiation of cDNA strand synthesis. The SpV4 genome was found to contain at least three promoterlike sequences quasi-identical to those of eubacteria. These results fully support the bacterial origin of spiroplasmas.

Amino Acid Sequence↗
PubMed1988

Nonstructural proteins nsP3 and nsP4 of Ross River and O'Nyong-nyong viruses: sequence and comparison with those of other alphaviruses.

We have sequenced the nsP3 and nsP4 region of two alphaviruses, Ross River virus and O'Nyong-nyong virus, in order to examine these viruses for the presence or absence of an opal termination codon present between nsP3 and nsP4 in many alphaviruses. We found that Ross River virus possesses an in-phase opal termination codon between nsP3 and nsP4, whereas in O'Nyong-nyong virus this termination codon is replaced by an arginine codon. Previous studies have shown that two other alphaviruses, Sindbis virus and Middelburg virus, possess an opal termination codon separating nsP3 and nsP4 [E.G. Strauss, C.M. Rice, and J.H. Strauss (1983), Proc. Natl. Acad. Sci. USA 80, 5271-5275], whereas Semliki Forest virus possesses an arginine codon in lieu of the opal codon [K. Takkinen (1986), Nucleic Acids Res. 14, 5667-5682]. Thus, of the five alphaviruses examined to date, three possess the opal codon and two do not. Production of nsP4 requires readthrough of the opal codon in those alphaviruses that possess this termination codon and the function of the termination codon may be to regulate the amount of nsP4 produced. It is an open question then as to whether alphaviruses with no termination codon use other mechanisms to regulate the activity of this gene. The nsP4s of these five alphaviruses are highly conserved, sharing 71-76% amino acid sequence similarity, and all five contain the Gly-Asp-Asp motif found in many RNA virus replicases. The nsP3s are somewhat less conserved, sharing 52-73% amino acid sequence similarity throughout most of the protein, but each possesses a nonconserved C-terminal domain of 134 to 246 amino acids of unknown function.

Alphavirus↗
PubMed1989

Translation affects immunoglobulin mRNA stability.

When termination codons were introduced into exons of the gene for Ig mu chain, steady-state levels of mu mRNA were reduced, both at the pre-B cell stage and at the plasma cell stage. A termination codon in the variable region gene segment and a termination codon in the second exon of the constant region gene segment had effects of similar magnitude. When the termination codon was deleted, the original level of mRNA was restored. The rate of mu gene transcription was the same whether or not a termination codon was present. Therefore, the termination codons must reduce the amount of the mRNA by reducing its stability. Since the introduced termination codons prematurely terminate translation and, in so doing, change the ribosome load on the mRNA, we conclude that mu mRNA stability is conferred in part by ribosomal protection from enzymatic degradation. We propose that the differences in mu mRNA stability during B lymphocyte differentiation are due to different amounts of ribosomes available for translation.

B-Lymphocytes↗
PubMed2001

Loss of cyp1a1 messenger rna expression due to nonsense-mediated decay.

Clones of the mouse hepatoma cell line Hepa1c1c7 (Hepa-1) with lesions in the Cyp1a1 gene were isolated previously. A subset of these clones fails to express CYP1A1 mRNA even when treated with 2,3,7,8-tetrachlorodibenzo-p-dioxin, which induces this mRNA in wild-type Hepa-1 cells. The current investigation sought an explanation for this phenotype in one of these clones, c33. Loss of mRNA expression in c33 was shown to be caused by mutational changes in the Cyp1a1 gene rather than by its epigenetic silencing. No mutations were identified in the 5' flanking region of the Cyp1a1 gene, containing the promoter and dioxin-responsive enhancer sequences. A single nucleotide insertion occurred at nucleotide 418 in the coding region of one Cyp1a1 allele, and a single nucleotide insertion occurred at nucleotide 465 in the other allele in c33. These sequence alterations were confirmed in the genomic DNA of the clone. Both insertions generate a premature termination codon at codon 172. This termination codon occurs in a position within the intron/exon structure of the Cyp1a1 gene such that the encoded mRNA should be subject to "nonsense-mediated decay" (NMD). Inhibition of protein synthesis is known to reverse NMD. The protein synthesis inhibitors cycloheximide and puromycin fully restored CYP1A1 mRNA expression to c33 cells, supporting the notion that NMD degrades CYP1A1 mRNA in this strain. The mutations identified in the coding region of c33 provide an explanation, therefore, for its loss of both CYP1A1 enzymatic activity and inducible CYP1A1 mRNA expression.

Animals↗
PubMed1983

The Shine and Dalgarno hypothesis for termination: the 3' terminus of the 16S rRNA of the Escherichia coli ribosome can be modified or base-paired with a complementary oligonucleotide without affecting termination in vitro.

The occurrence of the nucleotides "...CCUUAOH" at the 3' terminus of the 16S rRNA of the small subunit of the Escherichia coli ribosome led to the suggestion that they may have a direct base pairing with the termination codon in the termination event of protein biosynthesis (Shine and Dalgarno 1974). We have examined this concept with two approaches, firstly using a 30S subunit whose 16S rRNA has been modified with a fluorescein moiety on the terminal adenosine together with the antibody against the moiety, and secondly with an oligonucleotide, UAAGG, complementary to the terminal pentanucleotide sequence of the rRNA. Collectively the data suggest that the nucleotides at the 3' terminus of 16S rRNA are not critically involved in base pairing during termination codon recognition.

Base Composition↗
PubMed1989

On the role of the termination factor RF-2 and the 16S RNA in protein synthesis.

In the translational termination step of protein synthesis the three termination codons UAA, UAG or UGA are recognized by so-called release or termination factors. The release factor RF-1 interacts with UAG and UAA whereas RF-2 is specific for UGA and UAA. Two mechanisms concerning the termination event have been discussed so far: recognition of the termination codon by the protein in a tRNA-like manner or double-strand formation between the codon and the 3' end of the 16S rRNA which is stabilized by the termination factor. Using equilibrium dialysis we show that 40% of the ribosomes can bind UGAA in an RF-2-dependent manner. The stability with the correct combination RF-2-UGA is tenfold higher as compared to the wrong termination codon UAG. We confirm prior findings that the termination factor RF-2 is bound to the A-site of the ribosome. In addition to the ribosomal proteins L2, L10, L7/L12 and L20 of the large subunit and S6 and S18 of the small subunit, the 16S rRNA became labelled when radioactive UGA was crosslinked to the ribosome in the presence of RF-2. Our data support a mechanism of termination in which a double strand between the termination codon and the 3' end of the 16S rRNA is formed as the starting event. The resulting RNA-RNA double strand in turn may be recognized and stabilized by the termination factor.

Binding Sites↗
PubMed1992

DNA sequences required for translational frameshifting in production of the transposase encoded by IS1.

The transposase encoded by insertion sequence IS1 is produced from two out-of-phase reading frames (insA and B'-insB) by translational frameshifting, which occurs within a run of six adenines in the -1 direction. To determine the sequence essential for frameshifting, substitution mutations were introduced within the region containing the run of adenines and were examined for their effects on frameshifting. Substitutions at each of three (2nd, 3rd and 4th) adenine residues in the run, which are recognized by tRNA(Lys) reading insA, caused serious defects in frameshifting, showing that the three adenine residues are essential for frameshifting. The effects of substitution mutations introduced in the region flanking the run of adenines and in the secondary structures located downstream were, however, small, indicating that such a region and structures are not essential for frameshifting. Deletion of a region containing the termination codon of insA caused a decrease in beta-galactosidase activity specified by the lacZ fusion plasmid in frame with B'-insB. Exchange of the wild-type termination codon of insA for a different one or introduction of an additional termination codon in the region upstream of the native termination codon caused an increase in beta-galactosidase activity, indicating that the termination codon in insA affects the efficiency of frameshifting.

Amino Acid Sequence↗
PubMed1993

Non-standard translational events in Candida albicans mediated by an unusual seryl-tRNA with a 5'-CAG-3' (leucine) anticodon.

From in vitro translation studies we have previously demonstrated the existence of an apparent efficient UAG (amber) suppressor tRNA in the dimorphic fungus Candida albicans (Santos et al., 1990). Using an in vitro assay for termination codon readthrough the tRNA responsible was purified to homogeneity from C.albicans cells. The determined sequence of the purified tRNA predicts a 5'-CAG-3' anticodon that should decode the leucine codon CUG and not the UAG termination codon as originally hypothesized. However, the tRNA(CAG) sequence shows greater nucleotide homology with seryl-tRNAs from the closely related yeast Saccharomyces cerevisiae than with leucyl-tRNAs from the same species. In vitro tRNA-charging studies demonstrated that the purified tRNA(CAG) is charged with Ser. The gene encoding the tRNA was cloned from C.albicans by a PCR-based strategy and DNA sequence analysis confirmed both the structure of the tRNA(CAG) and the absence of any introns in the tRNA gene. The copy number of the tRNA(CAG) gene (1-2 genes per haploid genome) is in agreement with the relatively low abundance (< 0.5% total tRNA) of this tRNA. In vitro translation studies revealed that the purified tRNA(CAG) could induce apparent translational bypass of all three termination codons. However, peptide mapping of in vitro translation products demonstrated that the tRNA(CAG) induces translational misreading in the amino-terminal region of two RNA templates employed, namely the rabbit alpha- and beta-globin mRNAs. These results suggest that the C.albicans tRNA(CAG) is not an 'omnipotent' suppressor tRNA but rather may mediate a novel non-standard translational event in vitro during the translation of the CUG codon. The possible nature of this non-standard translation event is discussed in the context of both the unusual structural features of the tRNA(CAG) and its in vitro behaviour.

Anticodon↗
PubMed2003

Rapid detection of six common Mediterranean and three non-Mediterranean alpha-thalassemia point mutations by reverse dot blot analysis.

We describe the implementation of reverse dot blot (RDB) hybridization as a rapid nonradioactive method for the identification of six frequent globin gene point mutations in the Mediterranean population: alpha(Hph)alpha: alpha2 IVS I donor site GGTGAGG --> GG-----; alpha(NcoI)alpha: alpha2 initiation codon ATG --> ACG; alpha(TSaudi)alpha: alpha2Poly A signal AATAA --> AATAAG; alpha(Icaria)alpha: alpha2 termination codon TAA --> AAA (Ter --> LYS); alpha(CS)alpha: alpha2 termination codon TAA --> CAA (Ter --> gly); alphaalpha(NcoI): alpha1 initiation codon ATG --> GTG; and three alpha2 globin gene point mutations found in immigrants in Italy: alpha(T-Quongsze)alpha: alpha2 codon 12 CTG --> CCG (Leu --> Pro); alpha(Seal Rock)alpha: alpha2 termination codon TAA --> GAA (TER --> GLU); and alpha(Koyadora)alpha: alpha2 termination codon TAA --> TCA (TER --> SER). The method uses the principle of allele-specific oligonucleotide (ASO) hybridization, but it is a nonradioactive method and permits rapid and simultaneous typing of point mutations and small deletions.

Alleles↗
PubMed2003

Fabry disease: novel alpha-galactosidase A 3'-terminal mutations result in multiple transcripts due to aberrant 3'-end formation.

Mutations in the gene that encodes the lysosomal exoglycohydrolase, alpha-galactosidase A (alpha-GalA), cause Fabry disease, an X-linked recessive inborn error of glycosphingolipid catabolism. Human alpha-GalA is one of the rare mammalian genes that has its polyadenylation signal in the coding sequence and lacks a 3' untranslated region (UTR). We identified two novel frameshift mutations, 1277delAA (del2) and 1284delACTT (del4), in unrelated men with classical Fabry disease. Both mutations occurred in the 3' terminus of the coding region and obliterated the termination codon, and del2 also altered the polyadenylation signal. To characterize these mutations, 3' rapid amplification of cDNA ends (RACE) and polymerase chain reactions (PCR) were performed, and the amplicons were subcloned and sequenced. Both mutations generated multiple transcripts with various lengths of 3' terminal sequences, some elongating approximately 1 kb. Mutant transcripts were classified as follows: type I transcripts had terminal in-frame thymidines that created termination codons when polyadenylated, type II had downstream termination codons within the elongated alpha-GalA sequence, and type III, the most abundant, lacked termination codons at their 3' ends. To determine if the type III transcripts were degraded by the recently described cytosolic messenger RNA degradation pathway for messages lacking termination codons, northern blot analysis was performed. However, the finding of similar levels of nuclear and cytoplasmic alpha-GalA mRNA in normal and patient lymphoblasts suggested that mRNA degradation did not result from either mutation. Expression of representative transcript types revealed differences in intracellular localization and/or protein stability and catalytic activity, with most mutant proteins being nonfunctional. Characterization of these 3' mutations identified a novel molecular mechanism causing classical Fabry disease.

Amino Acid Sequence↗
PubMed1998

Discrimination of 5'-terminal start codons by translation initiation factor 3 is mediated by ribosomal protein S1.

The interrelation between ribosomal protein S1 and IF3 in recognition/discrimination of 5'-terminal start codons by 30S ribosomes has been studied using in vitro toeprinting. The study has been performed with two naturally occurring leaderless mRNAs, lambda cI and phage r1t rro mRNA, as well as with an artificial leaderless mRNA derived from the E. coli ompA gene. We show that in the absence of S1, IF3 does not discriminate against the authentic 5'-terminal start codon of both cI and rro mRNA. Since IF3 was able to exert its proofreading function for initiator tRNA(fMet) on 30S ribosomes lacking S1, this observation cannot be attributed to a lack of binding to or action of IF3 on 30S(-S1) ribosomes. In contrast to leaderless mRNAs, ternary complex formation occurs in the presence of IF3 with 30S ribosomes when the start codon is preceded by a short 20-nucleotide 5'-untranslated region containing a canonical Shine and Dalgarno sequence. This suggests that 5'-terminal start codons are recognised by IF3 as non-standard because of the lack of 16S rRNA-mRNA contacts.

Bacteriophage lambda↗
PubMed1978

Organization and expression of early genes of simian virus 40.

The early region of simian virus 40 codes for at least two immunologically related polypeptides: large-T and small-t, with apparent molecular weights of 90,000-100,000 and 15,000-20,000, respectively. Because small-t shares methionine-containing tryptic peptides with large-T, the two polypeptides are probably coded, in part, by a common nucleotide sequence. To locate the coding sequences for large-T and small-t in the DNA, the production of these proteins was examined after infection of CV-1 cells with wild-type and deletion mutants of simian virus 40. We found that a deletion at the distal portion of the early region alters the structure of large-T but not of small-t; but deletions within the region between map coordinates 0.59 and 0.55 result in an alteration or absence of small-t and a normal large-T. These findings have been rationalized by a model that proposes the existence of two early mRNAs, one coding for large-T and the other for small-t. Both mRNAs span virtually the entire early region; but the mRNA coding for large-T lacks the nucleotide sequence between map coordinates 0.59 and 0.54. We suggest that small-t is translated from the larger of the two mRNAs, beginning at or near its 5' end and terminating at a termination codon at about map coordinate 0.54. Larger-T, on the other hand, is translated from the shorter mRNA, beginning at the same initiator codon, and, because of the deletion of the terminator codon at 0.54, translation proceeds to the terminator codon at or near map position 0.18.

Antigens, Viral↗
PubMed2004

The case for nuclear translation.

Although it is frequently assumed that translation does not occur in eukaryotic nuclei, recent evidence suggests that some translation can take place and that it is closely coupled to transcription. The first evidence concerns the destruction of nuclear mRNAs containing premature termination codons by nonsense-mediated decay (NMD). Only ribosomes can detect termination codons, and as some NMD occurs within the nuclear fraction, active nuclear ribosomes could perform the required detection. The second evidence is the demonstration that tagged amino acids are incorporated into nascent polypeptides in a nuclear process coupled to transcription. The third evidence is that components involved in translation, NMD and transcription colocalize, coimmunoprecipitate and co-purify. All these results are simply explained if nuclear ribosomes scan nascent transcripts for premature termination codons at the site of transcription. Alternatively, the scanning needed for NMD might take place at the nuclear membrane, and contaminating cytoplasmic ribosomes might give the appearance of some nuclear translation. We argue, however, that the balance of evidence favours bona fide nuclear translation.

Animals↗
PubMed1996

Dual functions of ribosome recycling factor in protein biosynthesis: disassembling the termination complex and preventing translational errors.

We summarize in this communication the data supporting the two functions of ribosome recycling factor (RRF, originally called ribosome releasing factor). The first described role involves the disassembly of the termination complex which consists of mRNA, tRNA and the ribosome bound to the mRNA at the termination codon. This process is catalyzed by two factors, elongation factor G (EF-G) and RRF. RRF stimulated protein synthesis as much as eight-fold in the in vitro lysozyme synthesis system, when ribosomes were limiting. In the absence of RRF, ribosomes remain mRNA-bound at the termination codon and translate downstream codons. In the in vitro system, the site of reinitiation is the triplet codon 3' to the termination codon. RRF is an essential protein for bacterial life. Temperature sensitive (ts) RRF mutants were isolated and in vivo translational reinitiation due to inactivation of ts RRF was demonstrated using the beta-galactosidase reporter gene placed downstream from the termination codon. A second function of RRF involves preventing errors in translation. In polyphenylalanine synthesis programmed by polyuridylic acid, misincorporation of isoleucine, leucine or a mixture of amino acids was stimulated upto 17-fold when RRF was omitted from the in vitro system. RRF did not influence the large error (10-fold increase) induced by streptomycin. This means that RRF participates not only in the disassembly of the termination complex but also in peptide elongation. Extending this concept and its conventional role for releasing ribosomes from mRNA, involvement of RRF in the reinitiation in the 3A' system (a construct using S aureus protein A, a collaborative work with Dr Isaksson), in programmed frame shifting, in trans-translation with 10Sa RNA (collaborative work with Dr Muto), and in the reinitiation downstream from the ORF A of the IS 3 (insertion sequence of a transposon, collaborative work with Dr Sekine) are discussed on the basis of preliminary data to be published elsewhere. Finally, we review the known RRF sequences from various organisms including eukaryotes and discuss the possible mechanism for disassembly of the eukaryotic termination complex.

Bacteria↗
PubMed1981

Identification of an H-2Kb-related molecule by molecular cloning.

Based on the published amino-acid sequence of H-2Kb, we synthesized a mixture of eight 16-base long oligodeoxyribonucleotides representing all possible coding sequences for residues 51-56 (Trp-Met-Glu-Gln-Glu-Gly). The hexadecanucleotide mixture was used as a probe to screen recombinant DNA clones constructed from cytoplasmic PolyA+ RNA isolated from the murine thymoma cell line EL4(b haplotype). Of the 30 000 independent clones screened, one clone was found to hybridize with the probe. DNA sequence analysis showed that the cDNA clone was derived from a portion of an H-2Kb -related mRNA. The clone encodes a protein sequence identical with a region of H-2Kb in 42 consecutive residues (50 through 91). The sequence than diverges from the H-2Kb sequence and, after a single Glu codon, a termination codon is encountered. It is possible that this mRNA codes for a small 92 amino-acid protein with a sequence identical (except for a carboxy-terminal Glu residue) with the amino terminus of H-2Kb. It is further speculated that this mRNA is coded for by the H-2Kb gene and differs from the H-2Kb mRNA in the pattern of posttranscriptional splicing.

Amino Acid Sequence↗
PubMed1998

[Researches on the nucleotide sequencing of the recombinant Sj 22.6 kDa antigen gene of Schistosoma japonicum].

AIM: To sequence the cloned gene in pGSj24 and to identify the encoded protein. METHODS: The cloned gene in pGSj24 was digested from the recombinant plasmid by EcoRI, ligated into the M13mp19 vector and sequenced by automatic sequencer. The sequence was analyzed by Goldkey DNA and Protein Analytical Program and DNASIS Program. RESULTS: The pGSj24 cloned gene was demonstrated to be 840 bp containing one opened reading frame (ORF) with an initiation codon ATG at position 23 nt and a termination codon TAA at position 596 nt, encoding a protein with a molecular weight of 22.6 kDa. At the upstream and downstream of the ORF there were termination codons, so the encoded protein was unable to be larger. However, there was a termination codon TAA at position 11 nt, suggesting why the 22.6 kDa protein expressed separately. The nucleotide sequence of the pGSj24 cloned gene shared 95% identity with that of the corresponding part of S. japonicum 22.6 kDa antigen gene, and 99.7% identity in the encoding part. The deduced amino acid sequence analysis showed a sequence motif known as EF-Hand calcium binding domain, several endoplasmic reticulum targeting sequences and microbodies C-terminal targeting signals. The possible antigen determinants were predicted within the amino acid fragments of 29-32aa, 63-68aa and 87-101aa. CONCLUSIONS: The cloned gene in pGSj24 is the gene that encodes Sj22.6 kDa antigen.

Amino Acid Sequence↗
PubMed1994

Control of cationic amino acid transport and retroviral receptor functions in a membrane protein family.

A partial cDNA sequence indicated that the T lymphocyte early-activation gene (Tea) encodes a protein related to the dual-function ecotropic retrovirus receptor/cationic amino acid transporter (ecoR/CAT1), and RNA blots suggested highest Tea expression in T lymphocytes and liver (MacLeod, C.L., Finley, K., Kakuda, D. Kozad, C.A., and Wilkinson, M.F. (1990) Mol. Cell. Biol. 7, 3663-3674). The sequence of full-length Tea cDNA from liver (3683 bases) predicts a 657-amino-acid protein (CAT2 alpha) with 12-14 transmembrane domains. A long (515 base) region with six initiation codons and termination codons precedes the translation start codon. The liver Tea cDNA is identical to Tea cDNA from T lymphocytes (encoding CAT2 beta) with the exception of an apparent alternatively spliced sequence encoding a hydrophilic loop of 43 amino acids. The liver-specific sequence contains unique consensus sites for phosphorylation by cyclic AMP-dependent protein kinase and by protein kinase C. Injection of Xenopus oocytes with CAT2 alpha or CAT2 beta messenger RNA resulted in expression of Na(+)-independent cationic amino acid transport that was detected by current measurements under voltage-clamp. Although the amino acid sequences of the isoforms differ in only 21 of 43 residues with the majority of substitutions being conservative, the apparent affinity of CAT2 beta for arginine uptake was 70-fold higher than the CAT2 alpha isoform (Km 38 microM versus 2.7 mM). Neither isoform functioned as a receptor for ecotropic or amphotropic murine retroviruses. However, CAT1-CAT2 chimeric proteins that contain the first three putative extracellular loops of ecoR/CAT1 functioned as ecotropic receptors despite a diminished capacity to bind the viral envelope glycoprotein. The chimeric proteins also functioned as basic amino acid transporters with substrate affinities corresponding to the CAT2 isoform constituting the carboxyl-terminal portion. These results demonstrate that domains of these transporters can function in chimeric combinations to control viral receptor and transport functions.

Amino Acid Sequence↗