The cytokinin, N(6)-(Delta(2)-isopentenyl) adenosine occurs in the soluble RNA of yeast and mammalian tissue and has now been detected in plant soluble RNA. A hydroxylated derivative of this cytokinin 6-(cis-4-hydroxy-3-methylbut-2-enylamino)-9-,beta-D-ribofuranosylpurine has also been identified as a constituent of plant soluble RNA.

Isopentenyl adenosine derivatives are always located adjacent to the 3' end of the anticodon in transfer RNA and have been implicated in certain biological functions. In the enteric bacterium, E. coli, the derivative is ms2i6A whereas in some plant associated bacteria the derivative is the hydroxylated form, ms2io6A. Anti-i6A immunoadsorbent chromatography has been employed to detect isopentenyl adenosine compounds. In the present study we show that the transfer RNA of three species of enteric bacteria, S. typhimurium, K. pneumoniae, and S. marcescens contains both ms2io6A and ms2i6A. Under the growth conditions utilized the ms2io6A is predominant. The presence of ms2io6A in Enterobacteriacae is particularly noteworthy since in previous work it has been found only in plant-associated species of bacteria.

Transfer RNAs isolated from E. coli grown in media where ferric iron is not freely available show well characterized chromatographic changes due to the absence of the methylthio moiety of ms2i6A. The altered tRNA molecules include tRNA trp tRNA tyr, tRNA phe and two minor tRNA ser species. It has been suggested that methylthiolation of tRNA affects its function in regulation. We now show iron-related changes in tRNA trp from S. typhimurium, Ps. aeruginosa and K. pneumoniae. tRNA trp from S. typhimurium contains ms2i6A and it seems probable that the availability of iron affects the synthesis of ms2i6A-tRNA trp from i6A-tRNA trp in this organism. An iron-related methylthiolating system may also be operative in K. pneumoniae. S. marcescens tRNA trp, however was not affected by the availability of iron. Neither ms2i6A nor i6A was found in S. marcescens tRNA, although an, as yet unidentified, hydrophobic nucleoside was present.

A snake venom ribonuclease, similar to the classical pancreas ribonuclease, can be freed of other known nucleolytic activities by acid treatment, or by acetone-fractionation of Russell viper venom. Utilizing an end-group analytical technique in conjunction with oligonucleotide analyses of both partial and complete digests of ribonucleates, it has been possible to broadly characterize the mode of action of the snake venom ribonuclease, even though it is present in such small amount in venom that extensive purification was not attempted. The venom ribonuclease parallels pancreas ribonuclease in its acid stability, pH dependence, and high degree of preferential specificity toward PypA bonds in ribonucleate chains. Studies of the limited fragmentation of ribosomal and soluble ribonucleates, as well as dinucleoside phosphates, have shown that there are subtle differences between the venom and pancreas ribonucleases. The results of the investigation suggest that the venom and pancreas ribonucleases can be useful as a means of introducing a limited number of preferential scissions into ribonucleate chains at PypA internucleoside phosphodiester bonds. Incidental to the principal investigations dealing with the mode of action of the venom and pancreas ribonucleases on ribonucleates, certain features pertaining to the nucleotide sequences in ribosomal and soluble ribonucleates from wheat embryo have been noted.

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