Some of the base, sugar, and phosphate moieties in cellular ribonucleic acids are selectively modified in many instances. These posttranscriptional modifications in nucleic acids have important functions, such as increasing specificity, altering the ability of nucleic acids to base pair, affecting binding of proteins like transcription factors to DNA and thus regulating gene expression, etc. Transfer RNAs have been studied extensively for the function of posttranscriptional modifications. In addition to tRNAs, ribosomal RNAs, messenger RNAs, as well as small RNAs contain posttranscriptional modifications; over 90 different modifications have been identified in different RNAs (3). The fact that approximately 1% of the E. coli genome corresponds to the tRNA modifying enzymes and that these genes are retained through evolution would suggest that these modifications are functionally important [reviewed in Bjork et al. (1)]. In one instance, the gene for a tRNA modifying enzyme was shown to be essential for viability. This study showed that the methyluridine found in the conserved TΨC loop of the transfer RNA serves an essential function (6). Although no clear functional role has been suggested for any of the modified nucleotides in rRNA, their importance is evident by models of the E. coli ribosome in which the modifications are clustered around the mRNA–tRNA–peptide complex at the catalytic center of the ribosome (2). These suggestions are more relevant in light of Noller’s observation that peptidyl transferase activity is unusually resistant to protein extraction procedures, consistent with the hypothesis that rRNA itself is the catalytically active component of the ribosome (5). In one instance, the gene that is responsible for a ribose methylation at a universally conserved nucleotide in peptidyl transfer center of the ribosomal RNA was found to be essential for cell growth (7). These data show that modified nucleotides play important, and some times essential, roles in the rRNA function. While most cellular RNAs contain modified nucleotides, 5S ribosomal RNA from most species does not contain any modified nucleotides. During the last 20 years, there has been a rapid and exciting progress in elucidating the roles of small nuclear RNAs and small nucleolar RNAs (4,8,9). This special issue focuses on the biosynthesis and posttranscriptional processing and modification reactions that occur in small RNAs.
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Document Type: Miscellaneous
Publication date: January 1, 2002
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- Gene Expression, The Journal of Liver Research will publish articles in all aspects of hepatology. Hepatology, as a research discipline, has seen unprecedented growth especially in the cellular and molecular mechanisms of hepatic health and disease, which continues to have a major impact on understanding liver development, stem cells, carcinogenesis, tissue engineering, injury, repair, regeneration, immunology, metabolism, fibrosis, and transplantation. Continued research and improved understanding in these areas will have a meaningful impact on liver disease prevention, diagnosis, and treatment. The existing journal Gene Expression has expanded its focus to become Gene Expression, The Journal of Liver Research to meet this growing demand. In its revised and expanded scope, the journal will publish high-impact original articles, reviews, short but complete articles, and special articles (editorials, commentaries, opinions) on all aspects of hepatology, making it a unique and invaluable resource for readers interested in this field. The expanded team, led by an Editor-in-Chief who is uniquely qualified and a renowned expert, along with a dynamic and functional editorial board, is determined to make this a premier journal in the field of hepatology.