title: Simian virus 40 maturation: chromatin modifications increase the accessibility of viral DNA to nuclease and RNA polymerase.
abstract: The accessibility of extracellular and nuclear simian virus 40 (SV40-M and SV40-I, respectively) virion chromatin DNAs to micrococcal nuclease, DNase I, BglI, EcoRI, and RNA polymerase was examined. Our results support the following conclusions: (i) the intranucleosomal DNA of SV40-I chromatin, similar to the precursor 75S chromatin complex, is resistant to enzymatic activity; and (ii) SV40-M virion chromatin is modified in a manner which increases the accessibility of viral DNA to enzymes, and the distinction between nucleosomal DNA and linker DNA is absent. Micrococcal nuclease digestion of SV40-I virion chromatin gave a typical nucleosomal DNA ladder pattern with a repeat unit of 205 base pairs of DNA. SV40-I chromatin was sensitive to cleavage with endonuclease BglI, but not with EcoRI. When SV40-I virion chromatin was used as a template, the rate of incorporation of ribonucleoside triphosphates into RNA was 5% of that obtained with naked form SV40 form I DNA. Micrococcal nuclease digestion of SV40-M virion chromatin resulted in submonomeric DNA fragments of approximately 55 base pairs, but no larger repeating unit of DNA was observed. SV40-M virion chromatin was sensitive to cleavage with either BglI or EcoRI and was approximately 20% more susceptible to digestion with DNase I than was SV40-I virion chromatin. The transcriptional efficiency of the extracellular virion chromatin was almost equivalent to that of naked SV40 form I DNA and was 16-fold higher than the rate observed with nuclear virion chromatin. The increased transcriptional activity was dependent upon the presence of nonhistone viral protein VP1 or VP2 or both.
mesh_terms: D002843:Chromatin / Q000378:metabolism; D004262:DNA Restriction Enzymes / Q000378:metabolism; D004279:DNA, Viral / Q000378:metabolism*; D012321:DNA-Directed RNA Polymerases / Q000378:metabolism*; D015246:Deoxyribonuclease EcoRI; D003850:Deoxyribonuclease I; D003851:Deoxyribonucleases / Q000378:metabolism; D015252:Deoxyribonucleases, Type II Site-Specific; D004720:Endonucleases / Q000378:metabolism; D008836:Micrococcal Nuclease / Q000378:metabolism; D009707:Nucleosomes / Q000378:metabolism; D010727:Phosphoric Diester Hydrolases / Q000378:metabolism*; D013539:Simian virus 40 / Q000254:growth & development / Q000378:metabolism*
chemical_list: D002843:Chromatin; D004279:DNA, Viral; D009707:Nucleosomes; D012321:DNA-Directed RNA Polymerases; D003851:Deoxyribonucleases; D004720:Endonucleases; D004262:DNA Restriction Enzymes; D015246:Deoxyribonuclease EcoRI; D003850:Deoxyribonuclease I; D015252:Deoxyribonucleases, Type II Site-Specific; C018492:GCCNNNNNGGC-specific type II deoxyribonucleases; D008836:Micrococcal Nuclease; D010727:Phosphoric Diester Hydrolases