Biomedical subjects

R S Kumar

Publications and source records attributed to R S Kumar.

At least 37 records · Page 2Linked to original sources

PubMed1994

Identification of positive and negative transcriptional regulatory elements of the rabbit angiotensin-converting enzyme gene.

The two tissue-specific mRNAs encoding the isozymes of rabbit angiotensin-converting enzyme (ACE) are generated from the same gene by alternative choice of two transcription initiation sites 5.7 kb apart. In the current study, we have characterized the regulatory sites controlling the transcription of the larger pulmonary isozyme mRNA. For this purpose, reporter genes driven by varying lengths of upstream region of the ACE gene were transfected into ACE-producing cells. Our results demonstrated that the transcription of this gene is primarily driven by positive elements within the first 274 bp DNA upstream of the transcription initiation site. The reporter gene driven by this region was expressed in two ACE-producing cells but not in two ACE-non-producing cells thereby establishing its tissue specificity. Our experiments also revealed the existence of a strong negative element located between -692 and -610 positions. This element suppressed the expression of the reporter gene in a dose-dependent and position and orientation-independent fashion thus suggesting that it is a true silencer element. It could also repress the expression of a reporter gene driven by the heterologous strong promoter of the beta-actin gene. The repressing effects of the negative element could be partially overcome by cotransfecting the isolated negative element along with the reporter gene containing the negative element. This result was possibly due to the functional removal of a limiting trans-acting factor which binds to this element. Electrophoretic mobility shift assays revealed that the negative element can form several complexes with proteins present in the nuclear extract of an ACE-producing cell line. At least part of the negative element is strongly conserved in the upstream regions of the human and mouse ACE genes.

Animals↗

PubMed1994

Recovery from paraplegia following aortic saddle embolism. Case report.

An aortic saddle embolus causing paraplegia is rare and even rarer is a documentation of neurological recovery from this event. A 47 year old male presented with absent pulsations in the lower limbs and paraplegia, both of sudden onset. He underwent immediate bilateral transfemoral embolectomy. The postoperative period was stormy. The paraplegia recovered over a period of 2 months and he could walk to his place of work after 6 months. The rare combination of saddle embolus and paraplegia is discussed. An attempt has been made to verify the hypothesis of Dickson et al which states that a low origin of the great radicular artery (GRA) below T12 level may be responsible for paraplegia when obstructed by a saddle embolus. We found the GRA arising at L2 vertebral level in this patient. Postoperative selective spinal arteriogram and magnetic resonance imaging (MRI) of the spinal cord showed a patent GRA and normal spinal cord structure respectively. Early surgical intervention in restoring the blood flow into the GRA may prevent severe histological changes hitherto responsible for nonrecovery from paraplegia in the earlier reports.

Aortic Diseases↗

PubMed1993

Intracerebral polyposis. Case report.

A 25-year-old man presented with nontraumatic cerebrospinal fluid rhinorrhea and meningitis. On investigation, he was found to have a multiloculated intracerebral cystic lesion of the right frontal lobe with a bony lesion inside the cyst, just above the right cribriform plate. Surgery revealed multiple grape-like cystic pedunculated lesions with narrow stalks attached to a bony outgrowth which was adherent to the right cribriform plate. Macroscopically and microscopically, the excised lesions were similar to nasal polyps.

Adult↗

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