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At least 1,423 records · Page 79Linked to original sources
PubMed2003

Cloning and characterization of genes encoding trehalose-6-phosphate synthase (TPS1) and trehalose-6-phosphate phosphatase (TPS2) from Zygosaccharomyces rouxii.

In many organisms, trehalose protects against several environmental stresses, such as heat, desiccation, and salt, probably by stabilizing protein structures and lipid membranes. Trehalose synthesis in yeast is mediated by a complex of trehalose-6-phosphate synthase (TPS1) and trehalose-6-phosphate phosphatase (TPS2). In this study, genes encoding TPS1 and TPS2 were isolated from Zygosaccharomyces rouxii (designated ZrTPS1 and ZrTPS2, respectively). They were functionally identified by their complementation of the tps1 and tps2 yeast deletion mutants, which are unable to grow on glucose medium and with heat, respectively. Full-length ZrTPS1 cDNA is composed of 1476 nucleotides encoding a protein of 492 amino acids with a molecular mass of 56 kDa. ZrTPS2 cDNA consists of 2843 nucleotides with an open reading frame of 2700 bp, which encodes a polypeptide of 900 amino acids with a molecular mass of 104 kDa. The amino acid sequence encoded by ZrTPS1 has relatively high homology with TPS1 of Saccharomyces cerevisiae and Schizosaccharomyces pombe, compared with TPS2. Western blot analysis showed that the antibody against S. cerevisiae TPS1 recognizes ZrTPS1. Under normal growth conditions, ZrTPS1 and ZrTPS2 were highly and constitutively expressed, unlike S. cerevisiae TPS1 and TPS2. Salt stress and heat stress reduced the expression of the ZrTPS1 and ZrTPS2 genes, respectively.

Amino Acid Sequence↗
PubMed2005

Cloning and characterization of a gene encoding a malic enzyme involved in anaerobic growth in Mucor circinelloides.

A 3193 bp contiguous sequence has been cloned from the oleaginous fungus Mucor circinelloides, that contains a full-length gene encoding a putative NADP+: dependent malic enzyme (EC. 1.1.1.40). The cloned DNA contains a 2154 bp putative open reading frame containing five introns and encoding a protein of 616 amino acids. The gene encoded what appeared to be an anaerobic isoform of malic enzyme (isoform II); this conclusion is supported by transcript analysis and by the fact that the ORF contains an N-terminal mitochondrial target sequence (a similar cellular location was identified for the anaerobic malic enzyme in Saccharomyces cerevisiae; Boles et al. 1998). The cloned gene did not encode either isoform III (the isoform associated with active growth) or isoform IV (associated with lipid accumulation) previously identified. M. circinelloides therefore must possess (at least) two structural genes for malic enzyme.

Anaerobiosis↗
PubMed2007

Role of processing speed and depressed mood on encoding, storage, and retrieval memory functions in patients diagnosed with schizophrenia.

The role of various types of slowing of processing speed, as well as the role of depressed mood, on each stage of verbal memory functioning in patients diagnosed with schizophrenia was investigated. Mixed lists of high- and low-frequency words were presented, and immediate and delayed free recall and recognition were required. Two levels of encoding were studied by contrasting the relatively automatic encoding of the high-frequency words and the more effortful encoding of the low-frequency words. Storage was studied by contrasting immediate and delayed recall. Retrieval was studied by contrasting free recall and recognition. Three tests of motor and cognitive processing speed were administered as well. Regression analyses involving the three processing speed measures revealed that cognitive speed was the only predictor of the recall and recognition of the low-frequency words. Furthermore, slowing in cognitive speed accounted for the deficit in recall and recognition of the low-frequency words relative to a healthy control group. Depressed mood was significantly associated with recognition of the low-frequency words. Neither processing speed nor depressed mood was associated with storage efficiency. It is concluded that both cognitive speed slowing and depressed mood impact on effortful encoding processes.

Brain↗
PubMed2000

Identification of the TRM2 gene encoding the tRNA(m5U54)methyltransferase of Saccharomyces cerevisiae.

The presence of 5-methyluridine (m5U) at position 54 is a ubiquitous feature of most bacterial and eukaryotic elongator tRNAs. In this study, we have identified and characterized the TRM2 gene that encodes the tRNA(m5U54)methyltransferase, responsible for the formation of this modified nucleoside in Saccharomyces cerevisiae. Transfer RNA isolated from TRM2-disrupted yeast strains does not contain the m5U54 nucleoside. Moreover, a glutathione S-transferase (GST) tagged recombinant, Trm2p, expressed in Escherichia coli displayed tRNA(m5U54)methyltransferase activity using as substrate tRNA isolated from a trm2 mutant strain, but not tRNA isolated from a TRM2 wild-type strain. In contrast to what is found for the tRNA(m5U54)methyltransferase encoding gene trmA+ in E. coli, the TRM2 gene is not essential for cell viability and a deletion strain shows no obvious phenotype. Surprisingly, we found that the TRM2 gene was previously identified as the RNC1/NUD1 gene, believed to encode the yNucR endo-exonuclease. The expression and activity of the yNucR endo-exonuclease is dependent on the RAD52 gene, and does not respond to increased gene dosage of the RNC1/NUD1 gene. In contrast, we find that the expression of a trm2-LacZ fusion and the activity of the tRNA(m5U54)methyltransferase is not regulated by the RAD52 gene and does respond on increased gene dosage of the TRM2 (RNC1/NUD1) gene. Furthermore, there was no nuclease activity associated with a GST-Trm2 recombinant protein. The purified yNucR endo-exonuclease has been reported to have an NH2-D-E-K-N-L motif, which is not found in the Trm2p. Therefore, we suggest that the yNucR endo-exonuclease is encoded by a gene other than TRM2.

3' Untranslated Regions↗
PubMed1992

Two human liver cDNAs encode UDP-glucuronosyltransferases with 2 log differences in activity toward parallel substrates including hyodeoxycholic acid and certain estrogen derivatives.

Two human liver UDP-glucuronosyltransferase cDNA clones, HLUG25 [Jackson, M. R., et al. (1987) Biochem. J. 242, 581-588] and UDPGTh-2 [Ritter, J. K., et al. (1990) J. Biol. Chem. 266, 7900-7906] have previously been shown to encode isozymes active in the glucuronidation of hyodeoxycholic acid (HDCA) and certain estrogen derivatives (estriols and 3,4-catechol estrogens), respectively. Here we report that the UDPGTh-2-encoded isoform (udpgth-2) and the HLUG25-encoded isoform (udpgth-1) have parallel aglycon specificities. Following expression in COS-1 cells, each isoform metabolized three types of dihydroxy- or trihydroxy-substituted ring structures, including the 3,4-catechol estrogen (4-hydroxyestrone), estriol and 17-epiestriol, and HDCA, but the udpgth-2 isozyme is 100-fold more efficient than udpgth-1. udpgth-1 and udpgth-2 are 86% identical overall (76 differences out of 528 amino acids), including 55 differences in the first 300 amino acids of the amino terminus, a domain which confers isoform substrate specificity. The data indicate that a high level of conservation in the amino terminus is not required for the preservation of substrate selectivity. Analysis of glucuronidation activity encoded by UDPGTh-1/UDPGTh-2 chimeric cDNAs constructed at their common restriction sites, SacI (codon 297), NcoI (codon 385), and HhaI (codon 469), showed that nine amino acids between residues 385 and 469 are important for catalytic efficiency, suggesting that this region represents a domain which is critical for catalysis but distinct from that responsible for aglycon selection.(ABSTRACT TRUNCATED AT 250 WORDS)

Binding Sites↗
PubMed1991

A homologue of a nuclear-coded iron-sulfur protein subunit of bovine mitochondrial complex I is encoded in chloroplast genomes.

The chloroplast genomes of Marchantia polymorpha, Nicotiana tabacum, and Oryza sativa contain open reading frames (ORFs or potential genes) encoding homologues of some of the subunits of mitochondrial NADH:ubiquinone oxidoreductase (complex I). Seven of these subunits (ND1-ND4, ND4L, ND5, and ND6) are products of the mitochondrial genome, and two others (the 49- and 30-kDa components of the iron-sulfur protein fraction) are nuclear gene products. These findings have been taken to indicate the presence in chloroplasts of an enzyme related to complex I, possibly an NAD(P)H:plastoquinone oxidoreductase, participating in chlororespiration. This view is reinforced by the present work in which we have shown that chloroplast genomes encode a homologue of the 23-kDa subunit, another nuclear-encoded component of bovine complex I. The 23-kDa subunit is in the hydrophobic protein fraction of the enzyme, the residuum after removal of the flavoprotein and iron-sulfur protein fractions. The sequence motif CysXXCysXXCysXXXCysPro, which provides ligands for tetranuclear iron-sulfur centers in ferredoxins, occurs twice in its polypeptide chain and is evidence of two associated 4Fe-4S clusters. This is the only iron-sulfur protein identified so far in the hydrophobic protein fraction of complex I, and so it is possible that one of these centers is that known as N-2, the donor of electrons to ubiquinone. The sequence of the 23-kDa subunit is closely related to potential proteins, which also contain the cysteine-rich sequence motifs, encoded in the frxB ORFs in chloroplast genomes.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acid Sequence↗
PubMed1991

Characterization of a putative clone for the 67-kilodalton elastin/laminin receptor suggests that it encodes a cytoplasmic protein rather than a cell surface receptor.

The 67-kDa elastin binding protein shares many immunological and structural properties with the high-affinity 67-kDa tumor cell laminin receptor. Taking advantage of these similarities, we have screened a bovine cDNA library with a partial cDNA probe for the laminin receptor and have isolated and characterized a cDNA clone of 1038 bp that hybridizes to a single-size mRNA of 1.3 kb. The clone encodes a protein with a predicted molecular weight of 33K that lacks an N-terminal leader sequence, shows no posttranslational processing when translated in vitro in the presence of microsomes, and does not bind to elastin affinity columns. Although the bovine clone is nearly identical with clones encoding human and mouse proteins proported to be 67-kDa laminin receptor, physical and functional characteristics of the encoded protein suggest that it is a cytoplasmic protein that does not bind elastin. This finding calls into question the earlier conclusion that the clone encodes the 67-kDa receptor.

Amino Acid Sequence↗
PubMed1986

Human liver fibronectin complementary DNAs: identification of two different messenger RNAs possibly encoding the alpha and beta subunits of plasma fibronectin.

Human fibronectin polymorphism arises from variation in the C-terminal region [e.g., Sekiguchi, K., Siri, A., Zardi, L., & Hakomori, S. (1985) J. Biol. Chem. 260, 5105-5114]. In order to verify the chemical basis of the fibronectin polymorphism, cDNAs encoding the C-terminal region of human liver fibronectin have been isolated, sequenced, and compared with cDNAs encoding so-called "cellular fibronectin" (i.e., fibronectin produced by cultured cells in vitro). Among the five independent cDNAs thus isolated, two cDNAs, named pLF2 and pLF4, differed in the nucleotide sequence at the "type III connecting segment" (IIIcs) region. pLF4 contained 192 bases in this region whereas pLF2 completely lacked these bases. S1 mapping analysis indicated that both cDNAs with and without the 192 bases are faithful copies of two fibronectin mRNA species abundantly present in human liver. Comparison of the liver cDNAs with those coding for cellular fibronectin indicates that the latter cDNAs contain the 75-base and/or 93-base extra segments at the 5' and 3' boundaries of the 192-base IIIcs region. These extra segments have the consensus sequences for the 3' splice sites at their 3' ends, suggesting that fibronectin mRNAs with partial or complete deletion of the IIIcs sequence result from alternative splicing of a primary RNA transcript. Liver fibronectin cDNAs also lacked the 270-based "extra domain" (ED) segment present in some, but not all, cDNAs encoding cellular fibronectin. Thus, cellular fibronectin appears to have three extra peptide segments, encoded by the 75-base and 93-base segments in the IIIcs region and by the 270-base ED region, that are mostly absent in the liver fibronectin.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acid Sequence↗
PubMed1990

Ribosomal protein L35: identification in spinach chloroplasts and isolation of a cDNA clone encoding its cytoplasmic precursor.

We describe the isolation of spinach chloroplast ribosomal protein L35 and characterization of a cDNA clone encoding its cytoplasmic precursor. This protein was only recently identified in ribosomes, but the sequences of four L35 genes have now been reported and confirm its presence in eubacteria, chloroplasts, and cyanelles. Using N-terminal sequence data, oligonucleotides were designed and a cDNA library was screened. The nucleotide sequence of the cDNA clones shows that the spinach L35 protein is encoded as a precursor of 159 residues, comprising a mature protein of 73 residues and a transit peptide of 86 residues. The cleavage site for forming the mature protein is deduced to be Thr-Val-Phe-Ala decreases Ala-Lys-Gly-Tyr. The L35 protein in the photosynthetic organelle of the protozoan Cyanophora paradoxa is encoded in the organelle DNA [Bryant & Stirewalt (1990) FEBS Lett. 259, 273-280]. The corresponding gene has not been found in the chloroplast DNA of a lower plant (liverwort) and two higher plants. Our results demonstrate that the L35 protein in a higher plant (spinach) is encoded in the nucleus. This finding, in light of the endosymbiont hypothesis, suggests an organelle to nucleus transfer of the L35 gene at the evolutionary beginnings of land plants.

Amino Acid Sequence↗
PubMed1997

Isolation and characterisation of tobacco (Nicotiana tabacum) cDNA clones encoding proteins involved in magnesium chelation into protoporphyrin IX.

We have identified cDNA clones encoding the two Mg chelatase subunits CHL I and CHL H from tobacco (Nicotiana tabacum) by screening a cDNA library with homologous cDNA fragments from Arabidopsis thaliana. A full-length Chl I cDNA clone encodes a peptide with 426 amino acids. The entire cDNA sequence encoding 1382 amino acid long CHL H was obtained by extension of a truncated cDNA fragment using the 'rapid amplification of cDNA ends' (RACE) method. Both genes Chl I and Chl H were strongly expressed in young leaves and to a lesser extent in mature leaves. Only traces of both transcripts were found in flowering organs. Southern blot analysis suggests that CHL I is encoded by a single gene and CHL H most likely by several genes.

Blotting, Northern↗
PubMed1998

Characterization of a single soybean cDNA encoding cytosolic and glyoxysomal isozymes of aspartate aminotransferase.

A soybean cDNA clone, pSAT1, which encodes both the cytosolic and glyoxysomal isozymes of aspartate aminotransferase (AAT; EC 2.6.1.1) was isolated. Genomic Southern blots and analysis of genomic clones indicated pSAT1 was encoded by a single copy gene. pSAT1 contained an open reading frame with ca. 90% amino acid identity to alfalfa and lupin cytosolic AAT and two in-frame start codons, designated ATG1 and ATG2. Alignment of this protein with other plant cytosolic AAT isozymes revealed a 37 amino acid N-terminal extension with characteristics of a peroxisomal targeting signal, designated PTS2, including the modified consensus sequence RL-X5-HF. The second start codon ATG2 aligned with previously reported start codons for plant cytosolic AAT cDNAs. Plasmids constructed to express the open reading frame initiated by each of the putative start codons produced proteins with AAT activity in Escherichia coli. Immune serum raised against the pSAT1-encoded protein reacted with three soybean AAT isozymes, AAT1 (glyoxysomal), AAT2 (cytosolic), and AAT3 (subcellular location unknown). We propose the glyoxysomal isozyme AAT1 is produced by translational initiation from ATG1 and the cytosolic isozyme AAT2 is produced by translational initiation from ATG2. N-terminal sequencing of purified AAT1 revealed complete identity with the pSAT1-encoded protein and was consistent with the processing of the PTS2. Analysis of cytosolic AAT genomic sequences from several other plant species revealed conservation of the two in-frame start codons and the PTS2 sequence, suggesting that these other species may utilize a single gene to generate both cytosolic and glyoxysomal or peroxisomal forms of AAT.

Amino Acid Sequence↗
PubMed1998

A Brassica cDNA clone encoding a bifunctional hydroxymethylpyrimidine kinase/thiamin-phosphate pyrophosphorylase involved in thiamin biosynthesis.

We report the characterization of a Brassica napus cDNA clone (pBTHI) encoding a protein (BTHI) with two enzymatic activities in the thiamin biosynthetic pathway, thiamin-phosphate pyrophosphorylase (TMP-PPase) and 2-methyl-4-amino-5-hydroxymethylpyrimidine-monophosphate kinase (HMP-P kinase). The cDNA clone was isolated by a novel functional complementation strategy employing an Escherichia coli mutant deficient in the TMP-PPase activity. A biochemical assay showed the clone to confer recovery of TMP-PPase activity in the E. coli mutant strain. The cDNA clone is 1746 bp long and contains an open reading frame encoding a peptide of 524 amino acids. The C-terminal part of BTH1 showed 53% and 59% sequence similarity to the N-terminal TMP-PPase region of the bifunctional yeast proteins Saccharomyces THI6 and Schizosaccharomyces pombe THI4, respectively. The N-terminal part of BTH1 showed 58% sequence similarity to HMP-P kinase of Salmonella typhimurium. The cDNA clone functionally complemented the S. typhimurium and E. coli thiD mutants deficient in the HMP-P kinase activity. These results show that the clone encodes a bifunctional protein with TMP-PPase at the C-terminus and HMP-P kinase at the N-terminus. This is in contrast to the yeast bifunctional proteins that encode TMP-PPase at the N-terminus and 4-methyl-5-(2-hydroxyethyl)thiazole kinase at the C-terminus. Expression of the BTH1 gene is negatively regulated by thiamin, as in the cases for the thiamin biosynthetic genes of microorganisms. This is the first report of a plant thiamin biosynthetic gene on which a specific biochemical activity is assigned. The Brassica BTH1 gene may correspond to the Arabidopsis TH-1 gene.

Alkyl and Aryl Transferases↗
PubMed1997

Herpesvirus of turkeys homologue of HSV VP16 is structurally related to varicella zoster virus trans-inducing protein encoded by ORF 10.

Expression of the immediate-early genes of alpha-herpesviruses is stimulated by a family of trans-inducing factors represented by VP16 of HSV-1 and ORF10 gene product of VZV. We have identified and determined the nucleotide sequence of the UL48 gene encoding the herpesvirus of turkeys (HVT) homologue of HSV VP16. The gene maps to the BamHI-J fragment and appears to be expressed in a form of bicistronic transcript together with UL49. The deduced amino acid sequence of the protein encoded by HVT UL48 gene shows 55% identity with MDV UL48 gene product. Like the majority of related proteins in other alpha-herpesviruses, the protein encoded by HVT UL48 gene lacks the acidic C-terminal tail, known to possess the transactivation capacity of HSV VP16. Hydrophobic cluster analysis has revealed that its predicted domain composition is closely related to the transactivator protein encoded by ORF10 of VZV. However, the putative amino-terminal activation domain of the HVT homologue of HSV VP16 does not contain a typical horseshoe-like hydrophobic cluster found in other alpha-herpesvirus homologues, suggesting either that it acts as a transactivator via a different activation domain or that its transactivation potential is diminished.

Amino Acid Sequence↗
PubMed1998

The myxoma virus EcoRI-O fragment encodes the DNA binding core protein and the major envelope protein of extracellular poxvirus.

The nucleotide sequences of the myxoma virus gene homologs encoding the DNA binding core protein (MF17) and the major envelope protein of the extracellular poxvirus particle (MF13) have been localized to the myxoma virus 4 kB EcoRI-O fragment. The EcoRI-O fragment is located approximately 22 kb from the left end of the 163 kb DNA genome and encodes homologs of the F12L, F13L, F15L, F16L, F17R and E1L genes of the Copenhagen strain of vaccinia virus. The inferred amino acid sequences of the myxoma virus EcoRI-O encoded products have been compared to the protein databases to identify related proteins. The myxoma virus open reading frames MF12, MF15, MF16, MF17 and ME1 encode homologs of poxvirus specific proteins while the MF13 envelope protein also shares amino acid similarity with other poxvirus and cellular proteins.

Amino Acid Sequence↗
PubMed2002

Functional analysis of the Na+/H+ antiporter encoding genes of the cyanobacterium Synechocystis PCC 6803.

The role of putative Na+/H+ antiporters encoded by nhaS1 (slr1727), nhaS3 (sll0689), nhaS4 (slr1595), and nhaS5 (slr0415) in salt stress response and internal pH regulation of the cyanobacterium Synechocystis PCC 6803 was investigated. For this purpose the mutants (single, double, and triple) impaired in genes coding for Na+/H+ antiporters were constructed using the method of interposon mutagenesis. PCR analyses of DNA demonstrated that mutations in nhaS1, nhaS4, and nhaS5 genes were segregated completely and the mutants contained only inactivated copies of the corresponding genes. Na+/H+ antiporter encoded by nhaS3 was essential for viability of Synechocystis since no completely segregated mutants were obtained. The steady-state intracellular sodium concentration and Na+/H+ antiporter activities were found to be the same in the wild type and all mutants. No differences were found in the growth rates of wild type and mutants during their cultivation in liquid media supplemented with 0.68 M or 0.85 M NaCl as well as in media buffered at pH 7.0, 8.0, or 9.0. The expression of genes coding for Na+/H+ antiporters was studied. No induction of any Na+/H+ antiporter encoding gene expression was found in wild type or single mutant cells grown under high salt or at different pH values. Nevertheless, in cells of double and triple mutants adapted to high salt or alkaline pH some of the remaining Na+/H+ antiporter encoding genes showed induction. These results might indicate that some of Na+/H+ antiporters can functionally replace each other under stress conditions in Synechocystis cells lacking the activity of more than one antiporter.

Cyanobacteria↗
PubMed2003

New genes encoding subunits of a cytochrome bc1-analogous complex in the respiratory chain of the hyperthermoacidophilic crenarchaeon Sulfolobus acidocaldarius.

The soxL gene from Sulfolobus acidocaldarius (DSM 639) encodes a Rieske iron-sulfur protein. In this study we report the identification of two open reading frames in its downstream region. The first one, named soxN, codes for a membrane protein bearing a resemblance to the b-type cytochromes of the cytochrome bc1 and b6f complexes. The protein is predicted to contain at least 10 transmembrane helices and features the two conserved histidine pairs coordinating the heme groups of these cytochromes. The second open reading frame, named odsN, encodes a soluble protein of unknown function. The genomic region displays a complex transcription pattern. Northern blot and RT-PCR analyses revealed the presence of mono- and bi-cistronic transcripts as well as a tri-cistronic transcript of soxL and cbsAB, encoding the mono-heme cytochrome b558/566. Phylogenetic analyses of the genes of the soxLN pair and of other archaeal gene pairs encoding Rieske iron-sulfur proteins and b-type cytochromes revealed an identical branching patterns for both protein families, suggesting an evolutionary link of these genes provided by the functional interaction of the proteins. On the basis of the findings of this study and the previously studied properties of the soxL and cbsA proteins, we propose the occurrence of a novel cytochrome bc1-analogous complex in the membranes of Sulfolobus, consisting of the cytochrome b homolog soxN, the Rieske protein soxL, the high potential cytochrome cbsA, as well as the non-redox-active subunits cbsB and odsN.

Amino Acid Sequence↗
PubMed2003

Mothers' overreactive discipline and their encoding and appraisals of toddler behavior.

The relations of observed overreactive discipline with mothers' tendencies to notice negative, relative to positive, child behavior (preferential negative encoding), and mothers' negative appraisals of neutral and positive child behavior (negative appraisal bias), were examined in mothers of toddlers. The mothers rated both their own children's and unfamiliar children's behavior. Negative appraisal bias with respect to mothers' own (but not unfamiliar) children was related to mothers' overreactivity, independent of child misbehavior. Overreactivity was not related to mothers' preferential negative encoding either of their own or of unfamiliar children's behavior. However, in the case of mothers' own children, preferential negative encoding moderated the relation between negative appraisal bias and overreactive discipline, such that the negative appraisal bias-overreactivity relation was significant only in the context of high preferential negative encoding.

Child Behavior↗
PubMed1997

Sequence characterization of gamma-crystallins from lip shark (Chiloscyllium colax): existence of two cDNAs encoding gamma-crystallins of mammalian and teleostean classes.

gamma-Crystallin is a common lens protein of most vertebrate eye lenses and the major protein component in lenses of fishes and in many mammalian species during embryonic and neonatal stages. To facilitate the structural characterization of gamma-crystallin possessing extensive charge heterogeneity, a cDNA mixture was constructed from the poly(A)+ mRNA isolated from shark eye lenses, and amplification by polymerase chain reaction (PCR) was carried out to obtain cDNAs encoding multiple shark gamma-crystallins. Sequencing analysis of multiple positive clones containing PCR-amplified inserts revealed the presence of a multiplicity of isoforms in the gamma-crystallin class of this cartilaginous fish. It was of interest to find that two shark cDNA sequences coexist, one encoding gamma-crystallin (gamma M1) of high methionine content (15.5%) and the other encoding one (gamma M2) of low methionine content (5.1%), each corresponding to the major teleostean and mammalian gamma-crystallins, respectively. Comparison of protein sequences encoded by these two shark cDNAs with published sequences of gamma-crystallins from mouse, bovine, human, frog, and carp lenses indicated that there is about 61-80% sequence homology between different species of the piscine class, whereas only 47-66% is found between mammals and shark. A phylogenetic tree constructed on the basis of sequence divergence among various gamma-crystallin cDNAs revealed the close relatedness between shark gamma M2-crystallin and mammalian gamma-crystallins and that between shark gamma M1 and teleostean gamma-crystallins. The results pointed to the fact that ancestral precursors of gamma-crystallins were present in the sharp lens long before the appearance of modern-day mammalian and teleostean gamma-crystallins.

Amino Acid Sequence↗