Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:3.1.30.1 (S1 nuclease)
 3,660 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

In Chlamydomonas reinhardtii, the origin for chloroplast DNA replication, Ori A, overlaps the coding region for the chloroplast ribosomal protein Rpl16. In an in vitro DNA replication system that uses cloned Ori A as template, alteration of transcription across rpl16 affects replication activity. S1 nuclease protection mapping of cellular RNA derived from this region revealed multiple 5' and 3' ends, and several 3' ends were mapped within mini Ori A (224 bp), the core region for replication initiation. We also demonstrated that the protein fraction used in the in vitro DNA replication system contained an RNA processing activity responsible for the generation of multiple 3' ends. The 3' ends of some of the processed RNA species coincided with those of the cellular transcripts. Initiation of DNA replication in the in vitro system changed the abundance of some of the processed RNA species, and the S1 nuclease protection pattern generated by the 3' ends now mimicked that of the in vivo transcripts. We also monitored the pattern of 3' ends in cellular transcripts from the rpl16 region during gametogenesis--when the chloroplast DNA is under-replicated--and detected a change in transcript abundance that correlated with that seen in the in vitro study. Measurements of the template activity of mutants with targeted sequences change near the sites of processing also supported the notion that the processed transcripts play an important role in DNA replication.
 ...
PMID:The effects of transcription and RNA processing on the initiation of chloroplast DNA replication in Chlamydomonas reinhardtii. 1077 51

In chloroplasts, the control of mRNA stability is of critical importance for proper regulation of gene expression. The Chlamydomonas reinhardtii strain Delta26pAtE is engineered such that the atpB mRNA terminates with an mRNA destabilizing polyadenylate tract, resulting in this strain being unable to conduct photosynthesis. A collection of photosynthetic revertants was obtained from Delta26pAtE, and gel blot hybridizations revealed RNA processing alterations in the majority of these suppressor of polyadenylation (spa) strains, resulting in a failure to expose the atpB mRNA 3' poly(A) tail. Two exceptions were spa19 and spa23, which maintained unusual heteroplasmic chloroplast genomes. One genome type, termed PS+, conferred photosynthetic competence by contributing to the stability of atpB mRNA; the other, termed PS-, was required for viability but could not produce stable atpB transcripts. Based on strand-specific RT-PCR, S1 nuclease protection, and RNA gel blots, evidence was obtained that the PS+ genome stabilizes atpB mRNA by generating an atpB antisense transcript, which attenuates the degradation of the polyadenylated form. The accumulation of double-stranded RNA was confirmed by insensitivity of atpB mRNA from PS+ genome-containing cells to S1 nuclease digestion. To obtain additional evidence for antisense RNA function in chloroplasts, we used strain Delta26, in which atpB mRNA is unstable because of the lack of a 3' stem-loop structure. In this context, when a 121-nucleotide segment of atpB antisense RNA was expressed from an ectopic site, an elevated accumulation of atpB mRNA resulted. Finally, when spa19 was placed in a genetic background in which expression of the chloroplast exoribonuclease polynucleotide phosphorylase was diminished, the PS+ genome and the antisense transcript were no longer required for photosynthesis. Taken together, our results suggest that antisense RNA in chloroplasts can protect otherwise unstable transcripts from 3'-->5' exonuclease activity, a phenomenon that may occur naturally in the symmetrically transcribed and densely packed chloroplast genome.
 ...
PMID:Antisense transcript and RNA processing alterations suppress instability of polyadenylated mRNA in chlamydomonas chloroplasts. 1548 97


<< Previous 1 2