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Biomedical subjects

M K Roy

Publications and source records attributed to M K Roy.

45 records · Page 3Linked to original sources
PubMed1984

7S RNA, containing 5S ribosomal RNA and the termination stem, is a specific substrate for the two RNA processing enzymes RNase III and RNase E.

The 7S RNA, a precursor of 5S rRNA that contains 5S rRNA and the termination stem and loop, is a substrate for RNase E and is also a substrate for RNase III. The cleavage by RNase III is in the stem, 11 nucleotides downstream from the 3' end of the mature 5S rRNA and 8 nucleotides downstream from the RNase E cleavage site. Near the cleaved nucleotides there are three base pairs that appear in the same relative positions in most known RNase III cleavage sites. The large product of the RNase III cleavage reaction, which is a 5S rRNA that contains 11 extra nucleotides at the 3' end, is a substrate for RNase E. This suggests that the information for the 3'-end cleavage by RNase E resides mainly in the 5S rRNA itself. Using rnc rne strains, carrying the plasmid that leads to the accumulation of 7S RNA, we showed that the 7S RNA does not result from an RNase III cleavage but is apparently a proper transcription termination product.

Base Sequence↗
PubMed1983

Precursor nucleotides at the 5' end are not required for processing by RNase E at the 3' end of 5-S rRNA.

7-S RNA, a single-site substrate for the processing enzyme RNase E of Escherichia coli, consists of p5 rRNA (the precursors of 5-S RNA) and the 3'-end region of the rRNA transcript which is mainly a termination stem and loop. The 7-S RNA studied here was derived mainly from the rRNA gene cluster rrnD, carried in a multicopy plasmid. It contains four different populations of molecules that differ from each other at their 5' ends only: the shortest species has the 5' end of the mature 5-S rRNA, while the others are one, two and three nucleotides longer. The four different 5'-end forms were separated in a long sequencing gel. Processing of these forms and unfractionated 7-S RNA by RNase E in vitro, showed that all forms, even the shortest one, can be processed to p5 rRNA. Since the extra nucleotides at the 5' end of the molecule could be base-paired with the region of 7-S RNA where RNase E cuts, it is concluded that this double-stranded structure is not required for the action of RNase E in separating the 3' end of p5 rRNA from the termination stem.

Base Composition↗
PubMed1983

Purification and properties of ribonuclease E, an RNA-processing enzyme from Escherichia coli.

The Escherichia coli RNA-processing enzyme RNAase E was purified through a number of steps including isoelectrofocusing. The final fraction contained mainly a single polypeptide of 66 kDa. However, while all the steps in the purification yielded the same qualitative activity, the specific activity of fractions was decreased in the last steps of the purification. By combining the most-purified enzyme with earlier fractions from the purification, we could show that the cells could contain a factor that enhances RNAase E activity. The purified enzyme showed the same characteristics with respect to temperature optimum, pH and ionic requirements as less-purified preparations. Testing specific inhibitors we concluded that the enzyme requires SH groups, free amino groups, and either of the amino acids tryptophan, tyrosine, histidine or methionine for its activity.

Base Sequence↗
PubMed1983

7 S RNA: a single site substrate for the RNA processing enzyme ribonuclease E of Escherichia coli.

7 S RNA accumulates at non-permissive temperatures in an RNAase E strain containing the recombinant plasmid pJR3 delta which carries a single 5 S rRNA gene and expression sequences. 7 S RNA is a processing intermediate that contains the complete sequence of 5 S rRNA as well as a stem-and-loop structure encoded by the terminator of rrnD. 7 S RNA can be processed in vitro by RNAase E. Structural analysis of the products (5 S rRNA and the stem) of in vitro processing of 7 S RNA revealed that the cleavage site of RNAase E in 7 S RNA is 3 nucleotides downstream from the 3' end of the mature 5 S rRNA. The cleavage generates 3'-hydroxyl and 5'-phosphate termini.

Base Sequence↗
PubMed1983

Maturation of 5-S rRNA: ribonuclease E cleavages and their dependence on precursor sequences.

9-S RNA is a processing intermediate that accumulates in an RNase E- strain of Escherichia coli. It spans from the RNase III cleavage site, after 23-S rRNA, to the 3' end of the transcript and is derived from rRNA genes which do not contain tRNAs distal to 5-S rRNA. Here, we have studied the processing of 9-S RNA with ribonuclease E. RNase E cleaves 9-S RNA in two sites: one of these is three nucleotides upstream from the 5' end of 5-S rRNA, the other downstream from its 3' end. Both cleavages are probably introduced by the same enzyme, since both cleavages are thermolabile when an extract of a temperature-sensitive RNase E mutant was used for processing in vitro. In order to asses the role of 5' and 3' end precursor-specific sequences in the RNase E reaction, we isolated the molecules lacking nucleotides at the 5' or 3' end. Molecules having the 5' end of 9-S RNA but missing nucleotides from the 3' end (called 8-S RNA) were as good a substrate for RNase E as 9-S, RNA itself. However, molecules having the 3' end of 9-S RNA but the 5' end of p5 (called 7-S RNA), were less efficient substrates for RNase E. Finally, the removal of as little as seven nucleotides from the 5' end of 8-S RNA rendered it almost completely unsuitable as a substrate for RNase E.

Base Sequence↗
PubMed1982

Ribonuclease E is involved in the processing of 5-S rRNA from a number of rRNA transcription units.

Strains of Escherichia coli having a thermosensitive RNase E produce a number of 5-S ribosomal RNA precursors at a non-permissive temperature. One of these precursors, 9-S RNA, was reported earlier [Ghora, B.K. and Apirion, D. (1978) Cell, 15, 1055-1066]. Here we show the existence of additional precursors to 5-S rRNA, originating from a number of rRNA genes. All the precursors are very similar in the first 200 nucleotides and the last part of this sequence contains the mature 5-S rRNA. Precursors that contain only these nucleotides (8-S RNA) accumulate. They probably originate from the rrn genes C, D and F which contain trailer tRNAs. The 9-S RNA precursors contain in addition a termination stem and loop structure and are derived from genes which do not contain trailer tRNA (Singh and Apirion, unpublished results). In addition, a 10-S precursor was identified. It contains distal to the 5-S rRNA a trailer tRNA, tRNAAsp, and a transcription termination signal. It is derived from the rrnF gene. The accumulation of an RNA precursor containing an RNase P site in an rne mutant suggests that the efficiency of one RNA processing enzyme depends on the activity of other RNA processing enzymes.

Base Composition↗
PubMed1976

[A new pigmented antibiotic from a soil streptomycete].

An antibiotic designated A28 was isolated from a soil streptomycete which showed wide antibacterial activity. The antibiotic was extracted and purified into a yellow powder. Its physico-chemical and antimicrobial properties indicated that it is a novel peptide antibiotic.

Anti-Bacterial Agents↗