Biomedical subjects

R S Kumar

Publications and source records attributed to R S Kumar.

18 recordsLinked to original sources

PubMed1992

Use of alternative polyadenylation sites for tissue-specific transcription of two angiotensin-converting enzyme mRNAs.

The pulmonary isozyme of rabbit angiotensin-converting enzyme (ACE) is encoded by an mRNA of about 5 kb. cDNA clones corresponding to different parts of this mRNA have been isolated and the complete nucleotide sequences of both the coding and non-coding regions of the mRNA have been determined. The encoded protein has 1309 residues with a 33 amino acids-long signal peptide at the amino terminus and a potential membrane-anchoring domain near the carboxyl terminus. There is a strong sequence homology between two regions of the rabbit cDNA and between the rabbit, human, and mouse cDNAs. Comparison of the nucleotide sequences of the 3' untranslated regions of rabbit pulmonary and testicular ACE cDNAs revealed that the testicular cDNA is nested within the pulmonary cDNA at the 3' end. A rabbit genomic clone encompassing this region was isolated and partially sequenced. It was shown that the gene contains two potential polyadenylation sites 628 bp apart within one exon. Northern analyses with an appropriate oligonucleotide probe confirmed that the proximal polyadenylation site is used exclusively for terminating the testicular mRNA whereas the distal one is used exclusively for the pulmonary mRNA. These results demonstrated that the transcription of the two mRNAs encoding the two ACE isozymes not only initiates at two alternative tissue-specific sites which are 5.7 kb apart but the mRNAs also get polyadenylated at two alternative sites which are 628 bp apart.

Amino Acid Sequence↗

PubMed1991

The mRNAs encoding the two angiotensin-converting isozymes are transcribed from the same gene by a tissue-specific choice of alternative transcription initiation sites.

The two tissue-specific isozymes of angiotensin-converting enzyme are encoded by two mRNAs. The 5-kilobase pulmonary mRNA (mRNAP) and the 2.5-kilobase testicular mRNA (mRNAT) have identical sequences near their 3'-ends, whereas each has a unique sequence toward its 5'-end. Here we report that the two mRNAs originate from the same gene by initiation of transcription at two alternative sites. We have isolated a rabbit genomic clone which encodes these mRNAs. The sequence organization of the genome is such that the unique sequence of mRNAP precedes that of mRNAT, which in turn precedes the sequence common to both species. For generation of mRNAP, the mRNAT-specific sequence is eliminated as an intron from the primary transcript by splicing. Transcription of mRNAT, on the other hand, initiates within this intron at the middle of the gene. The exact initiation sites of mRNAT and mRNAP have been determined by DNA sequencing; DNA, oligonucleotide, and antisense RNA protection assays; and primer extension assays. Analyses of the sequence upstream of the transcription initiation sites revealed the presence of putative binding sites of several known transcription factors including SP-1, AP-2, and IID.

Amino Acid Sequence↗

PubMed1990

Angiotensin-converting enzyme: structural relationship of the testicular and the pulmonary forms.

Angiotensin-converting enzyme exists in two isozymic forms that are encoded by two mRNAs. Recently, the complete primary structures of the testicular isozymes from rabbit and human and of the pulmonary isozymes from mouse and human have been determined. We report here the cloning of a portion of the cDNA for the rabbit pulmonary isozyme by using the polymerase chain reaction. The sequence of this cDNA was identical to the sequence of the corresponding portion of rabbit testicular cDNA. This observation suggests that the two mRNAs are transcribed from the same gene. Comparison of the structures of the enzyme isolated from different species is useful for identifying the functional constraints on the evolutionary changes of its structure.

Amino Acid Sequence↗

PubMed1989

Structure of testicular angiotensin-converting enzyme. A segmental mosaic isozyme.

The complete amino acid sequence of rabbit testicular angiotensin-converting enzyme has been deduced from the sequence of the corresponding cDNA clone. A protein of the expected molecular weight of 84,000 was translated in vitro from the mRNA encoded by this cDNA. All of the previously determined sequences of seven tryptic peptides from the enzyme are present in the deduced sequence, thus confirming the identity of the protein. From the deduced sequence it appears that the protein contains a signal peptide at the amino terminus and a hydrophobic anchoring domain near the carboxyl terminus. Northern analysis with oligonucleotide probes, whose sequences represented different regions of the cDNA, revealed not only the regions of extensive homology between the mRNAs encoding the testicular and the pulmonary isozymes but also a stretch of sequence near the 5' end unique to the testicular mRNA.

Amino Acid Sequence↗

PubMed1983