| Popis: |
After nuclear 4.5 S RNA was obtained in an electrophoretically homogenous state by preparative electrophoresis on polyacrylamide gels, it was separated by chromatography on DEAE-Sephadex into three peaks, the last of which contained 4.5 S RNAiii. The 4.5 S RNAiii is an extranucleolar nuclear species not found in the cytoplasm. The present study demonstrates that nuclear 4.5 S RNAiii is a unique RNA species with adenosine 3',5'-diphosphate residue (pAp) as the 5'-terminal and 2'-O-methyl uridine as the 3'-terminal nucleoside. It has a very low Tm of 37.5°. Its molecular weight is approximately 28,000 based upon mobility in polyacrylamide gels and 5'-terminal analyses. Analysis of the alkali-resistant dinucleotides showed that the 4.5 S RNAiii contains four alkali-resistant dinucleotides, i.e., adenosine 2'-O-methyl-3'-phosphoryl adenosine 3'-phosphate (AmpAp), guanosine 2'-O-methyl-3'-phosphoryl adenosine 3'-phosphate (GmpAp), and 2 guanosine 2'-O-methyl-3'-phosphorylguanosine 3'-phosphate residues (Gmp-Gp). After hydrolysis with pancreatic RNase, analysis of oligonucleotide frequencies indicates that most of the molecule is cleaved into mono- to tetranucleotides, i.e. only 18% remaining in larger fragments. Compared with other 4–7 S nuclear RNAs, the isotope distribution in these oligonucleotides differs in that the percentage is lower in uridine and higher in AAAC. |
