DNA homology of two Mycoplasma species

Formylatable methionine transfer RNA from Mycoplasma: purification and comparison of partial nucleotide sequences with those of other prokaryotic initiator tRNAs

The major species of the formylatable methionine tRNA from Mycoplasma mycoides var capri has been purified. The 5'- and 3'-terminal sequences of the purified tRNA are pC-G- and C-A-A-C-C-AOH, respectively. Thus, this tRNA also contains the unique structural feature found in two other prokaryotic initiator tRNAs in that the first nucleotide at the 5'-end cannot form a Watson-Crick type of base-pair to the fifth nucleotide from the 3'-end. The Mycoplasma tRNA does not contain ribothymidine; however, a specific uridine residue in the sequence G-U-psi-C-G- can be enzymatically methylated by E. coli extracts to yield G-T-psi-C-G. Since ribothymidine is absent in crude tRNA from this strain of Mycoplasma, the absence of T is probably due to the lack of a U yields T modifying enzyme.

Biosynthetic precursors of some modified nucleosides in the transfer ribonucleic acid of Mycoplasma mycoides var. capri

The ribosomal and transfer ribonucleic acid (tRNA) from Mycoplasma mycoides var. capri, grown in a medium containing uridine-((14)C)-5'-triphosphate and cytidine-(5-(3)H)-5'-triphosphate, were isolated and separated. The uridine in both species of RNA was shown to contain (14)C and the cytidine to contain both (3)H and (14)C. Comparison of the labeling of 4-thiouridine and pseudouridine, obtained from an enzymatic digest of the RNA, indicates that their biosynthetic precursor is uridine, not cytidine. It is probable that ribothymidine and dihydrouridine have the same derivation.