The autodegradation of ribonucleoprotein in Escherichia coli

Publisher Website
Google Scholar
Abstract
Most of the ribonucleic acid (RNA)-depolymerase activity of E. coli is present in a fraction (RII) which sediments between 25 000 and 78 000 g and contains the bulk of the RNA. In an undialysed suspension of disrupted dividing cells or a suspension that has been dialysed in the presence of more than 2 mM nagnesium chloride, the breakdown of RNA is inhibited by mM Mg2+ ion at pH 5.5-6.5 and I 0.15. At I 0.5, 5 mM Mg2+ ion is required for stability. Two routes of breakdown at pH 7.5 and 37[degree] can be distinguished the M route in the presence of Mg++ and the V route in its absence. The M route occurs at pH 7.5-8.5 in the presence of 1-2 mM Mg2++ ion at I 0.15 and is stimulated by orthophosphate. The nucleotide end products are mainly nucleoside 5''-phosphates. The V route occurs at pH 6.5-7.5 when ethylenediaminetetra-acetic acid is present. Nucleoside 2'':3 ''-cyclic phosphates are produced and these are further hydrolysed to nucleoside 3''-phosphates. The RNA becomes unstable when the concentration of magnesium is allowed to fall below 2 mM at I 0.15. The instability might be the result of the RNA breaking at the uridine and guanine residues to form 2'':3''-cyclic phosphate end groups. The RNA in the ribonucleoprotein fraction (RII) behaves in a similar way to RNA in an unf ractionated preparation of disrupted cells both with respect to conditions for optimum stability at pH 6 and in its ability to breakdown by more than one route at pH 7.5.