The DNA sequences of the entire structural H4, H3, H2A and H2B genes and of their 5' flanking regions have been determined in the histone DNA clone h19 of the sea urchin Psammechinus miliaris. In clone h19 the polarity of transcription and the relative arrangement of the histone genes is identical to that in clone h22 of the same species. The histone proteins encoded by h19 DNA differ in their primary structure from those encoded by clone h22 and have been compared to histone protein sequences of other sea urchin species as well as other eukaryotes. A comparative analysis of the 5' flanking DNA sequences of the structural histone genes in both clones revealed four ubiquitous sequence motifs; a pentameric element GATCC, followed at short distance by the Hogness box GTATAAATAG, a conserved sequence PyCATTCPu, in or near which the 5' ends of the mRNAs map in h22 DNA and lastly a sequence A, containing the initiation codon. These sequences are also found, sometimes in modified version, in front of other eukaryotic genes transcribed by polymerase II. When prelude sequences of isocoding histone genes in clone h19 and h22 are compared areas of homology are seen to extend beyond the ubiquitous sequence motifs towards the divergent AT-rich spacer and terminate between approximately 140 and 240 nucleotides away from the structural gene. These prelude regions contain quite large conservative sequence blocks which are specific for each type of histone genes.
The 3' flanking sequences of all five histone genes have been sequenced in the histone DNA clone h19 of the sea urchin Psammechinus miliaris. A large (23 bp) and a small (10 bp) conserved sequence was found by sequence comparison, some 29-40 bp downstream from the termination codon. 12 bases of the larger homology block show a dyad symmetry. The available sequences of clone h22 of the same species and those of the histone clones pSp2 and pSp17 of Strongylocentrotus purpuratus, another sea urchin species, fit well into this comparison. Two types of sequences are involved in the dyad symmetry; one is H1, H3 and H4 specific, the other is H2A and H2B specific. If these conserved sequences are transcribed, a hairpin loop could form in the RNA molecules. This secondary structure might serve as a recognition signal for a regulatory protein.
Two out of seven meningiomas tested in early cell cultures by indirect immunofluorescence staining showed simian virus 40 (SV40)-related tumor (T) antigen. In one tumor 90% of the cells were positive. An additional SV40-related antigen (U) was found in 10% of cells of a third tumor. These findings indicate that the meningioma cells showing a positive reaction are transformed by a papova virus that has at least partly the same antigenic properties as SV40 virus. SV40-related viral capsid (V) antigen was absent in all the meningiomas tested. No virus infectious for African green monkey kidney (AGMK) cells could be isolated. The tumors positive for T and U antigens showed the chromosome aberration typical for human meningiomas, i.e., the loss of one chromosome, G-22. The T-antigen-positive tumors showed further hypodiploidization. Experiments to rescue virus from the T-antigen-positive meningioma cells were performed: fusion of cells pretreated with 8-azaguanine with cells permissive for SV40 led to a low percentage (0.01-0.05%) of V-antigen-positive nuclei in heterokaryon cultures. On the basis of these results, the possibility of a correlation between the meningioma, a relatively common intracranial tumor in man, and an SV40-related papova virus must be considered. It remains to be shown whether this virus is a causative agent for human meningiomas.
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