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J M Abraham

Publications and source records attributed to J M Abraham.

At least 55 records · Page 3Linked to original sources
PubMed1989

RNA editing: the creation of nucleotide sequences in mRNA--a minireview.

RNA editing changes the nucleotide sequence of mRNAs that are encoded in genes which contain the sequences in an abbreviated form. Editing adds uridines that are not encoded in the gene to the transcripts and less frequently removes encoded uridines. The process appears to be posttranscriptional and to proceed in the 3'-to-5' direction. Some sites may undergo multiple editings until the final sequence is produced; in some cases uridines may be added and subsequently removed. A general hypothesis is proposed that predicts a series of reactions that may occur in association with a macromolecular complex, the editosome, which interacts with a multinucleotide region.

Animals↗
PubMed1988

Characterization of cytochrome c oxidase III transcripts that are edited only in the 3' region.

The cytochrome c oxidase subunit III (COIII) transcript of T. brucei is extensively edited by the addition and deletion of uridines. We have identified partially edited COIII RNAs; they have unedited 5' and edited 3' regions. Transcripts with edited 5' but unedited 3' regions were not detected. The partially edited RNAs may be editing intermediates. The junctions of unedited and edited sequences in cDNAs differ from both the DNA and fully edited mRNA sequences over a multinucleotide region. The partially edited RNAs could arise from several processes, but it seems likely that editing proceeds in the 3' to 5' direction.

Animals↗
PubMed1988

Extensive editing of the cytochrome c oxidase III transcript in Trypanosoma brucei.

The gene for cytochrome oxidase subunit III (COIII) is not detected in T. brucei by nucleotide sequence analysis or by cross-hybridization studies. We have identified the COIII transcript in the T. brucei mitochondrion by RNA and cDNA sequencing. Its nucleotide and predicted amino acid sequences are very similar to those from the COIII genes in related species. A mitochondrial DNA sequence that matches the COIII transcript, except for the absence of numerous thymidines, is located upstream of the apocytochrome b gene, the position of the COIII gene in related species. We conclude that this sequence is the COIII gene and that over 50% of the T. brucei COIII transcript sequence is created by RNA editing.

Amino Acid Sequence↗
PubMed1986

Fimbrial phase variation and DNA rearrangements in uropathogenic isolates of Escherichia coli.

Having previously shown that the oscillating on-off expression (phase variation) of type 1 fimbriae in Escherichia coli is regulated genetically by an invertible element of DNA, we wished to determine whether E. coli isolates recovered from infected humans behaved in similar fashion. We examined four different clinical isolates that expressed type 1 fimbriae, P fimbriae, or both. Using, in Southern blot analysis, a DNA probe from the type 1 fimbrial switch, that hybridized to one DNA band from phase-on bacteria and to two DNA bands from phase-off bacteria, we found that the three clinical isolates expressing type 1 fimbriae contained the same invertible switch previously seen in the K-12 isolate. Employing a similar approach to characterize the on-off expression of P fimbriae, we used a DNA probe containing the known transcriptional signals for P fimbriae. Although we detected DNA rearrangement in the two strains expressing P fimbriae, unlike the case for type 1 fimbriae, the rearrangement did not correlate with the on-off state of the P fimbriae. Rather, the DNA rearrangement correlated with the environmental conditions of growth of the bacteria from which the DNA was isolated. These results confirm the notion that P fimbriae expression and type 1 fimbriae expression are controlled differently.

DNA, Bacterial↗
PubMed1985

An invertible element of DNA controls phase variation of type 1 fimbriae of Escherichia coli.

The expression of type 1 fimbriae (pili) of Escherichia coli is turned on and off at the transcriptional level at a high frequency (10(-3) per cell per generation) in a process termed phase variation. Using Southern blot and DNA sequence analysis, we have detected a genomic rearrangement in the switch region immediately upstream of the fimbrial structural gene. This rearrangement involves an invertible 314-base-pair segment of DNA whose alternating orientation apparently results in the on-and-off activation of a promoter that determines the state of fimbrial expression.

Base Sequence↗
PubMed1985

Genetic analysis of the phase variation control of expression of type 1 fimbriae in Escherichia coli.

Expression of type 1 fimbriae in Escherichia coli exhibits phase variation, whereby individual cells can alternate between states of organelle expression (Fim+) and nonexpression (Fim-). Strains with a fimD-lac operon fusion, in which lac, rather than fimD, expression is under the control of the fimD promoter, undergo Lac+ in equilibrium Lac- phase variation, instead. After positioning a lambda prophage adjacent to the operon fusion, we were able to isolate specialized lambda phage carrying both the fimD-lac fusion and the phase variation control region. Introduction of such phage into an Fim+ strain resulted in construction of a strain with a double, independently switching phenotype (Fim+ in equilibrium Fim- and Lac+ in equilibrium Lac-), demonstrating that the region controlling phase variation is contiguous with the fimD-lac operon fusion and is cis acting. When the specialized lambda phage was propagated on a delta lac delta fim strain, phase variation occurred within the plaques, confirming that the phase variation control region is carried on the specialized transducing phage. All lysogens acquired the Lac+ in equilibrium Lac- phenotype, except for two nonswitching Lac+ recombinants, which acquired Lac+ in equilibrium Lac- phase variation only by trans complementation with fim. Phase variation of type 1 fimbriae, therefore, appears to involve both a cis-active element, which is cloned on a specialized lambda phage, and a trans-active permissive factor, which is not present on the phage, but rather must be supplied by the recipient strain in the transduction.

Escherichia coli↗
PubMed1981

Analysis of a restriction endonuclease map for bovine papillomavirus type 2 DNA.

A physical map was constructed for bovine papillomavirus type 2 DNA by the use of restriction endonucleases. A comparison between the genomes of bovine papillomavirus types 1 and 2 in regard to location and number of cleavage sites of seven enzymes is also presented. This comparison revealed similarities between the two genomes.

Bovine papillomavirus 1↗