ISOLATION FROM RAT-LIVER AND SEQUENCE OF A RNA FRAGMENT CONTAINING 32 NUCLEOTIDES FROM POSITION-5 TO POSITION-36 FROM 3' END OF RIBOSOMAL 18S RNA

Crude tRNA isolated from rat liver by the method of Rogg et al. (Biochem. Biophys. Acta 195, 13-15 1969) contains N6-dimethyl-a denosine (m26A) and was therefore fractionated in order to identify the m26A-containing RNAs. A unique species of RNA was purified which contained all the m26A present in the crude tRNA. Sequence analysis by postlabeling with γ-32P-ATP and polynucleotide kinase revealed that this RNA represents the 32 nucleotidesAAGGUUUCU(C)GUAGGUGm26Am26ACCUGCGGAAGGAUCfrom position 5 to 36 of the 3′ terminus of ribosonal 18S RNA. The 36 nucleotide long sequence from the 3′ end of rat liver 18S rRNA exhibits extensive homology with the corresponding sequence of E. coli 16S rRNA and with the 21 nucleotide long 3′ terminal equence so far known from Saccharomyces carlsbergensis 17S rRNA. A heterogeneity in this sequence provides the first evidence on the molecular level for the existence of (at least) two sets of redundant ribosomal 18S RNA genes in the rat. © 1978 Information Retrieval Limited 1 Falconberg Court London W1V5FG England.