At least five supermethylated nDNA families have been found in HeLa cells. The concentration of 5-methylcytosine increases on palindromes from 1 to 5 hours during the nDNA duplicative phase, decreasing again at the 6th hour of S. The early S-phase involves the accumulation of 5-methylcytosines on the nDNA sequences reassociating near a Cot = 3 x 10(-1). Late S involves increment of this base on the sequences which reassociate near a Cot = 9 x 10(-1) and Cot = 7 x 10(1). The unique sequences show a moderate methylation from 3 to 6 hours of S. This information shows that genes are methylated with an order during the S-phase in a system in which nDNA organization, modification and replication appear to be severely subordinated one to another. The possible role of methylation of foldback nDNA in regulation of transcription during the eukaryotic cell life cycle is discussed.
A model of rearrangement of 32S pre-rRNA during processing was proposed. The first step of these events is the cotranscriptional interaction of the 3'-half of 5.8S rRNA and adjacent part of the internal transcribed spacer (ITS-2) with the 3'-part of the small nucleolar U3RNA from its 155th to 215th nucleotides (numbered for a rat U3RNA). This interaction prevents formation of intramolecular double-stranded structure between 5'-and 3'-end sequences of 5.8S rRNA. The second step is the appearance of extended hairpin structures in the ITS-2, which leads to a compactisation of the entire 32S-pre-rRNA molecule and to the complex formation between 5.8S rRNA and 28S rRNA sequences as the result of U3RNA displacing. After elimination of ITS-2 sequences from 32S pre-rRNA this complex can be included into ribosomes.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.