Disease relevance of rnhA

• By screening a library of E. coli DNA for clones that suppressed RNase H deficiency of an E. coli rnh mutant, a clone was obtained that produced a protein with RNase H activity [1].
• Curing the cells of the lambda rnh prophage left the cell with an inactive rnh gene and resulted in cell death [2].
• A strain was made with two copies of the rnh gene by lysogenizing an E. coli strain with a lambda phage bearing a copy of the rnh gene [2].
• Because models predict exonucleolytic processing of the cleaved recipient leading to homologous strand invasion of the donor allele, the assay was performed in wild-type and exonuclease-deficient (rnh or dexA) phage [3].

High impact information on rnhA

• Xer site-specific recombination at natural plasmid recombination sites (e.g., cer in ColE1) is preferentially intramolecular, converting dimers to monomers [4].
• We have also coupled our mutations with lesions in dnaA, which is required for cell-cycle-specific DNA replication, and rnh (the gene for RNase H), which is required for specificity in the DNA initiation reaction, and determined the effects of the double and triple mutants under permissive and nonpermissive conditions [5].
• The Xer site-specific recombination system acts at ColE1 cer and pSC101 psi sites to ensure that these plasmids are in a monomeric state prior to cell division [6].
• Resolution of ColE1 dimers requires a DNA sequence implicated in the three-dimensional organization of the cer site [7].
• Plasmid pBR322 was found to replicate in rnh mutants in the absence of DNA polymerase I, the polA gene product, which is normally required for replication of this plasmid [8].

Chemical compound and disease context of rnhA

• Role of cysteine residues in ribonuclease H from Escherichia coli. Site-directed mutagenesis and chemical modification [9].
• The Escherichia coli arginine repressor (ArgR) controls expression of the arginine biosynthetic genes and acts as an accessory protein in Xer site-specific recombination at cer and related plasmid recombination sites [10].
• In contrast, two independent cer insertions into pBR329 did not stabilize the plasmid completely in E. coli F-18 Col- in vitro, and feeding the strain to streptomycin-treated mice resulted in rapid segregation of the plasmids in vivo [11].
• Recombinant sin-pro-pep was synthesized in Escherichia coli, refolded from 8 M urea, and purified [12].
• The alternative pathway of DNA replication in rnh mutants of Escherichia coli can be continuously initiated in the presence of chloramphenicol, giving rise to constitutive stable DNA replication (cSDR) [13].

Biological context of rnhA

• rnh (formerly termed sdrA) mutants of Escherichia coli K-12, capable of continuous DNA replication in the absence of protein synthesis (stable DNA replication), are devoid of ribonuclease H (RNase H, EC 3.1.26.4) activity [8].
• When a chimeric construct between pBR322 and pSC101 was introduced into a polA rnh double mutant, the replication of the plasmid via the pBR322 replicon was inhibited if the plasmid also carried an rnh+ gene or if the host harbored an F' plasmid carrying an rnh+ gene [8].
• The 5' terminus of the rnh RNA overlaps about 100 and 20 nucleotide sequences with the 5' terminus of the dnaQ-1 and dnaQ-2 RNA, respectively [14].
• The gene for Escherichia coli ribonuclease H has been studied by use of a plasmid which contains a segment of the E. coli chromosome [15].
• Of the two possible double-stranded structures, the shorter does not interfere with a likely rnh ribosome binding site, while the longer one does [16].

Anatomical context of rnhA

• 30S ribosomal subunits, 70S ribosomes or polysomes from E. coli were subjected to mild ultraviolet irradiation, and the 3'-terminal region of the 16S RNA was excised by 'addressed cleavage' using ribonuclease H in the presence of suitable complementary oligodeoxynucleotides [17].

Associations of rnhA with chemical compounds

• Stopped-flow experiments at sub-zero temperatures in the presence of 30% ethylene glycol allowed us to monitor the evolution of the scattering pattern, including the characteristic scattering peak in an s (=2 sin theta/lambda) range of 0.01-0.06 A-1 [18].
• A Gly residue inserted between alpha-helices B and C appears to relieve unfavorable interactions in the transition state and alternate conformer(s) and represents an important adaptation to adjust conformational changes within RNase H for activity at high temperatures [19].
• RP1-S2 retains carbenicillin and tetracycline resistances as well as loci that cause either the loss of P plasmids (incp) or a locus specifying susceptibility to curing (sinp) in the presence of a P plasmid [20].

Other interactions of rnhA

• From beta-galactosidase levels it was estimated that the promoter for dnaQ is 5 times more active than that for rnh [21].
• These strains contained a second unlinked mutation in either mutL or mutS or sin [22].
• This observation indicated that in B. subtilis both the rnhB and rnhC products are involved in certain essential cellular processes that are different from those suggested by E. coli rnh mutation studies [23].
• The results indicate that the cer-like site of pHS-2, like the ColE1 cer site, acts as a recA-independent, site-specific recombination site involved in the resolution of multimers, requiring the presence of the host-encoded factors ArgR, PepA, XerC, and XerD [24].

Analytical, diagnostic and therapeutic context of rnhA

• rnh mutants harboring pBR322 were found to contain several slowly migrating DNA species when examined by agarose gel electrophoresis [25].
• Sequence analysis of hybrids indicates that recombination involving cer and ckr is site-specific and occurs within a 35 bp region of DNA which contains palindromic symmetry [26].

References