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)

Ribonucleotide reductase (RR) activity in mammalian cells is closely linked to DNA synthesis. The RR enzyme is composed of two non-identical subunits, proteins R1 and R2. Both proteins are required for holoenzyme activity, which is regulated by S-phase specific de novo synthesis and breakdown of the R2 subunit. In quiescent cells stimulated to proliferate and in elutriated cell populations enriched in the various cell cycle phases the R2 protein levels are correlated to R2 mRNA levels that are low in G0/G1-phase cells but increase dramatically at the G1/S border. Using an R2 promoter-luciferase reporter gene construct we demonstrate an unexpected early activation of the R2 promoter as cells pass from quiescence to proliferation. However, due to a transcriptional block, this promoter activation only results in very short R2 transcripts until cells enter the S-phase, when full-length R2 transcripts start to appear. The position for the transcriptional block was localized to a nucleotide sequence approximately 87 bp downstream from the first exon/intron boundary by S1 nuclease mapping of R2 transcripts from modified in vitro nuclear run-on experiments. These results identify blocking of transcription as a mechanism to control cell cycle regulated gene expression.
 ...
PMID:An S-phase specific release from a transcriptional block regulates the expression of mouse ribonucleotide reductase R2 subunit. 146 20

Ribonucleotide reductase has been suggested as a rate-limiting enzyme in DNA synthesis, partly because activities of the enzyme in cell-free preparations are low relative to rates needed to sustain DNA replication at observed rates. Vaccinia virus, with a large duplex DNA genome, encodes both subunits of a specific ribonucleoside diphosphate reductase. In this report, we describe quantitative analysis of ribonucleotide reductase protein levels and DNA accumulation in vaccinia virus-infected cell extracts, to correlate the supply of deoxyribonucleotides with the demand for these precursors in viral DNA synthesis. To do this, we generated polyclonal antisera to TrpE fusion proteins constructed from the carboxyl termini of both subunits of viral ribonucleotide reductase. We used S1 nuclease and immunoprecipitation analysis to determine the transcriptional and translational kinetics of vaccinia virus ribonucleotide reductase expression. Enzyme activity and ribonucleotide reductase protein stability were also assayed during the time course of viral infection. Enzyme-linked immunoassays were used to quantitate protein levels, and filter hybridizations were used to measure the accumulation of viral DNA. We show that ribonucleotide reductase activity in vaccinia virus-infected cells is severalfold higher than needed to provide deoxyribonucleotides at rates commensurate with DNA synthesis. Thus, while the enzyme is important as catalyst for the first committed reaction in DNA replication, it is not rate-limiting for this process.
 ...
PMID:Vaccinia virus ribonucleotide reductase. Correlation between deoxyribonucleotide supply and demand. 846 52