Читать книгу Snyder and Champness Molecular Genetics of Bacteria - Tina M. Henkin - Страница 164

There are two major classes of RNases (Table 2.1 and Figure 2.18). Endoribonucleases cleave the sugar-phosphate backbone of the RNA within the RNA chain to generate two smaller RNA products, one with a 3′ hydroxyl and the other with a 5′ monophosphate. Exoribonucleases digest the RNA processively, removing 1 nucleotide at a time, starting at a free end. Most organisms have multiple endo- and exoribonucleases, and some subtypes of these enzymes are found in many different organisms, while others are present in only certain groups of organisms. In E. coli, all exoribonucleases that have been identified bind to the 3′ end of an RNA substrate and digest the RNA in a 3′-to-5′ direction. In contrast, Bacillus subtilis and a number of other organisms contain both 3′-5′ exoribonucleases and 5′-3′ exoribonucleases. At least one of the B. subtilis 5′-3′ RNases (RNase J2) has both exoribonucleolytic and endoribonucleolytic activities (Table 2.1).