rnr Gene from the Antarctic Bacterium Pseudomonas syringae Lz4W, Encoding a Psychrophilic RNase R▿†

• Published in: Applied and Environmental Microbiology
• Main Authors: Sulthana, Shaheen, Rajyaguru, Purusharth I., Mittal, Pragya, Ray, Malay K.
• Format: Text
• Language: English
• Published: American Society for Microbiology 2011
• Subjects: Genetics and Molecular Biology; Antarctic; The Antarctic; Antarc*
• Online Access: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3208988; http://www.ncbi.nlm.nih.gov/pubmed/21926201; https://doi.org/10.1128/AEM.05683-11

RNase R is a highly processive, hydrolytic 3′-5′ exoribonuclease belonging to the RNB/RNR superfamily which plays significant roles in RNA metabolism in bacteria. The enzyme was observed to be essential for growth of the psychrophilic Antarctic bacterium Pseudomonas syringae Lz4W at a low temperature. We present results here pertaining to the biochemical properties of RNase R and the RNase R-encoding gene (rnr) locus from this bacterium. By cloning and expressing a His6-tagged form of the P. syringae RNase R (RNase RPs), we show that the enzyme is active at 0 to 4°C but exhibits optimum activity at ∼25°C. The enzyme is heat labile in nature, losing activity upon incubation at 37°C and above, a hallmark of many psychrophilic enzymes. The enzyme requires divalent cations (Mg2+ and Mn2+) for activity, and the activity is higher in 50 to 150 mM KCl when it largely remains as a monomer. On synthetic substrates, RNase RPs exhibited maximum activity on poly(A) and poly(U) in preference over poly(G) and poly(C). The enzyme also degraded structured malE-malF RNA substrates. Analysis of the cleavage products shows that the enzyme, apart from releasing 5′-nucleotide monophosphates by the processive exoribonuclease activity, produces four-nucleotide end products, as opposed to two-nucleotide products, of RNA chain by Escherichia coli RNase R. Interestingly, three ribonucleotides (ATP, GTP, and CTP) inhibited the activity of RNase RPs in vitro. The ability of the nonhydrolyzable ATP-γS to inhibit RNase RPs activity suggests that nucleotide hydrolysis is not required for inhibition. This is the first report on the biochemical property of a psychrophilic RNase R from any bacterium.