The Occurrence of Two Nicks in the Heavy Chloroplast Ribosomal RNA of Nicotiana rustica

Abstract

Newly synthesized 1.1 x 10 6 mol. wt. chloroplast ribosomal RNA molecules of Nicotiana rustica are unbroken polynucleotide chains. These molecules are stable during extraction and during electrophoresis under fully denaturing conditions in 6 M urea. During post-maturation of the 1.1 x 10 6 mol. wt. RNA two nicks are formed successively. At first the RNA is cleaved into two fragments with mol. weights of 0.7 and 0.4 x 10 6 , and in a second step the 0.7 x 10 6 mol. wt. fragment is further cleaved into two fragments of mol. weights 0.5 and 0.2 x 10 6 . In older, 6-8 cm long leaves the newly synthesized heavy chloroplast rRNA remains more stable (at least 18 h) than in young, 2-3 cm long leaves where nicking begins already few hours after RNA synthesis.