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Biomedical subjects

S Penman

Publications and source records attributed to S Penman.

At least 145 records · Page 8Linked to original sources
PubMed1973

Mitochondrial protein synthesis: RNA with the properties of Eukaryotic messenger RNA.

A heterogeneous RNA fraction with properties resembling those of messenger RNA was identified in mammalian mitochondria. Synthesis of contaminating RNA of nuclear origin was suppressed by treatment with camptothecin. Labeling of the messenger-like RNA is completely inhibited by ethidium bromide, a specific inhibitor of mitochondrial functions.Although mitochondrial protein synthesis resembles that of prokaryotes in several regards, the messenger-like RNA is covalently linked to poly(adenylic acid) [poly(A)]. Poly(A) has thus far been found only in eukaryotic cells. The poly(A) segment has a gel electrophoretic mobility of about 4 S, corresponding to a length of 50-80 nucleotides, and thus resembles in size the poly(A) found in some mammalian viral RNAs. The messenger RNA can be released from the mitochondrial protein-synthesizing structure by treatment with puromycin.

Adenine↗
PubMed1973

Stimulation of polypeptide initiation in vitro after protein synthesis inhibition in vivo in HeLa cells.

Crude cytoplasmic extracts prepared from HeLa cells actively incorporate amino acids but show little initiation of new peptides (as seen by labeling of N-terminal amino acids). In contrast, extracts prepared from cells subjected to prior inhibition of protein synthesis show a significant amount of polypeptide initiation indicated by formation of peptides with radioactive N-terminal methionine. The same result was obtained whether prior inhibition occurred with cycloheximide or by starvation for an essential amino acid. Cellular response to suppression of protein synthesis appears to be mediated through production of RNA, since it is inhibited by actinomycin but appears in the presence of cycloheximide. The crude extracts continue initiating new polypeptides for at least 10 min in vitro. It is postulated that enhancement of in vitro initiation described here is related to the apparent stimulation of initiation of translation seen in vivo.

Amino Acids↗
PubMed1972

Transcription of the adenovirus genome by an -amanitine-sensitive ribonucleic acid polymerase in HeLa cells.

The properties of the ribonucleic acid (RNA) polymerase activity which transcribes the major portion of the adenovirus genome were studied. Nuclei were prepared from infected cells and incubated in vitro. Virus-specific RNA was determined by hybridization to adenovirus deoxyribonucleic acid (DNA). Adenovirus DNA is transcribed principally by an activity which resembles closely polymerase II of the host cell. This activity is inhibited by alpha-amanitine and stimulated by (NH(4))(2)SO(4). Its product is high-molecular-weight heterogeneous RNA. The polymerase activity measured early in infection (3 to 5 hr) resembles that found late in infection (16 to 18 hr).

Adenoviridae↗
PubMed1971

Synthesis of 5S and 4S RNA in metaphase-arrested HeLa cells.

The continued synthesis of both 5S and 4S RNA in metaphase-arrested HeLa cells is demonstrated; 5S RNA is apparently synthesized at approximately 74 percent of the interphase rate, while 4S RNA is synthesized at approximately one-third the rate. The ratio of uridine incorporation to RNA methylation is used to correct for the alteration in the specific activity of the pyrimidine pool during metaphase arrest.

Carbon Isotopes↗
PubMed1971

Products of RNA polymerases in HeLa cell nuclei.

RNA polymerase activities in intact HeLa cell nuclei have been examined and compared to activities investigated in previous studies of the purified enzymes. The RNA synthesized by the mammalian polymerases while still in nuclei is identified. The polymerases are tentatively identified by location, sensitivity to alpha-amanitin, and response to manganese and altered ionic strength. Polymerase I is located in the nucleolus and labels partially complete precursor molecules of ribosomal RNA. Polymerases II and III are in the nucleoplasm and both label giant nuclear heterogeneous RNA.

Cell Nucleus↗