Molecular weight determination of precursor, mature and post-mature plastid ribosomal RNA from spinach using fully denaturing conditions

Abstract

RNA is extracted from purified plastids isolated from young leaves of spinach and is electrophoresed in fully denaturing conditions with 98% of formamide in the gels. The 16 S and 23 S rRNA of Escherichia coli were used as internal standards. The plastid 16 S rRNA is made of unbroken polynucleotide chains ( M r = 0.535 ± 0.005 · 10 6; the value of 0.54 · 10 6 is used). Some of the molecules of the 23 S rRNA are also unbroken polynucleotide chains of 1.28 ± 0.03 · 10 6 daltons while the others are composed of several fragments connected together by hydrogen bonding. Some of these fragments are detected in large relative amounts with the following M r : 0.71 ± 0.01 · 10 6; 0.43 ± 0.01 · 10 6; 0.35 ± 0.01 · 10 6 and 0.15 ± 0.01 · 10 6; others are detected in low relative amounts with the following M r: 0.98 ± 0.03 · 10 6 and 0.27 ± 0.02 · 10 6. All these fragments results from the denaturation in formamide of the nicked (post-matured) 23 S molecules. The determination of M r of each species has been done with isolated molecules of 23 S and 16 S rRNA. The M r of p23 S and of p16 S are respectively 1.54 ± 0.03 · 10 6 and 0.7 · 10 6. The newly synthesized 23 S molecules have a M r of 1.28 ± 0.03 · 10 6 (unbroken polynucleotide chain). The post-maturation of the 23 S is demonstrated by a pulse-chase experiment.