All sequenced histidine tRNAs have one additional nucleotide at the 5' end when compared to other tRNA species. Sequence analysis of histidine tRNA genes from Drosophila melanogaster and Schizosaccharomyces pombe showed that the terminal guanylate residue of the mature tRNAs is not encoded by the genes. Analysis of the products from in vitro transcription of these genes in extracts from Drosophila Kc cells demonstrated that the 5'-terminal nucleotide present in the mature tRNA is added post-transcriptionally. The addition reaction requires ATP. A portion of the mature tRNAs are then modified at the 5'-terminal pG. Analysis of the RNA species formed during the in vitro maturation of the Drosophila histidine tRNA primary transcript uncovered the following maturation scheme: (i) the primary transcript is processed by RNase P at the 5' end to form an intermediate precursor; (ii) the 3'-flanking sequence is endonucleolytically removed, and a guanylate moiety is added to the 5' end to form mature-sized histidine tRNA; and (iii) a fraction of the 5'-terminal guanylate residues then undergoes modification. In contrast to the capping of eukaryotic mRNA, the guanylate addition to histidine tRNA results in the formation of a (3'-5')-phosphodiester bond. There are no precedents for the post-transcriptional addition of nucleotides (in phosphodiester linkage) to the 5' end of RNA precursors.
We compared two isogenic FA cell lines: HSC536N (mock), a FA type C cell line sensitive to mitomycin C (MMC), and the same cell line transfected (corrected) with wild-type FAC cDNA (HSC536N [+FAC]). HSC536N (+FAC) cells showed a 30-fold increase in resistance to MMC concentration. Similarly, increas...
HIV has long served as a model for viruses that enter cells by direct fusion at the plasma membrane. Miyauchi et al. (2009) now provide compelling evidence that HIV enters cells primarily by endocytosis.
Pubget Updates sends you emails when Pubget finds new papers that match your search. Use Pubget Updates to get the latest articles for your specialty, written by a colleague, or published by your favorite journals.