Hensgens L A, Van der Horst G, Grivell L A
Plasmid. 1984 Jul;12(1):41-51. doi: 10.1016/0147-619x(84)90065-9.
The effects of mutations have been studied within the apocytochrome b gene on the processing of transcripts from the gene for subunit 1 of cytochrome c oxidase (coxI). Most mutations which affect the expression of the reading frame encoded by the fourth intron of the apocytochrome b gene (bI4) result in a failure to remove intron aI4 from precursor transcripts of coxI. Mutations in other apocytochrome b introns result in additional and complex defects in the processing of subunit I transcripts. Mutants M1233 and M1282 are mutated within the second intron (bI2) of the apocytochrome b gene and have OXI3 transcripts of 4900, 6100, and 6500 nucleotides. These transcripts are absent from the wild-type strain and do not hybridize with all exon sequences of this gene. In mutant M1392 (mutated within the third intron of the apocytochrome b gene), two OXI3 transcripts of 2200 and 2800 nucleotides are present which hybridize only with sequences downstream of the fifth exon of this gene (A5 alpha). We propose that all these transcripts result from distinctive cut-no-splice events, occurring at different intron-exon borders of OXI3 pre-RNAs depending on the mutational site within the apocytochrome b gene. The box9 mutant M4458 and the box7 mutant M1431 lack detectable 18S mRNA for subunit I of cytochrome c oxidase. The box9 mutants M4751 and M4701 contain reduced amounts of this mRNA. The fact that these loci complement each other (B. Weiss-Brummer, G. Rödel, R.J. Schweyen, and F. Kaudewitz (1982) Cell 29, 527-536), therefore, suggests that mutations within the different functional domains of bI4 lead to different defects in the processing of OXI3 transcripts. This, together with the defects observed in bI2 and bI3 mutants, implies that the box effect (i.e., the interaction between these two split genes) is not mediated by the box7 element alone. The possibility is discussed that mutated apocytochrome b intronic reading frame products lead to these aberrant events in the processing of transcripts of the gene for subunit I of cytochrome c oxidase.
已经研究了脱辅基细胞色素b基因内的突变对细胞色素c氧化酶亚基1基因（coxI）转录本加工的影响。大多数影响脱辅基细胞色素b基因第四内含子（bI4）编码阅读框表达的突变会导致无法从coxI前体转录本中去除内含子aI4。脱辅基细胞色素b其他内含子中的突变会导致亚基I转录本加工出现额外且复杂的缺陷。突变体M1233和M1282在脱辅基细胞色素b基因的第二个内含子（bI2）内发生突变，其OXI3转录本分别为4900、6100和6500个核苷酸。野生型菌株中不存在这些转录本，并且它们与该基因的所有外显子序列均不杂交。在突变体M1392（脱辅基细胞色素b基因的第三个内含子内发生突变）中，存在两种分别为2200和2800个核苷酸的OXI3转录本，它们仅与该基因第五外显子（A5α）下游的序列杂交。我们提出，所有这些转录本均源自独特的切割但不拼接事件，这些事件发生在OXI3前体RNA的不同内含子 - 外显子边界，具体取决于脱辅基细胞色素b基因内的突变位点。box9突变体M4458和box7突变体M1431缺乏可检测到的细胞色素c氧化酶亚基I的18S mRNA。box9突变体M4751和M4701中该mRNA的含量减少。这些位点相互互补的事实（B. Weiss - Brummer，G. Rödel，R.J. Schweyen和F. Kaudewitz（1982年）《细胞》29卷，527 - 536页），因此表明bI4不同功能域内的突变会导致OXI3转录本加工出现不同缺陷。这与在bI2和bI3突变体中观察到的缺陷一起，意味着盒效应（即这两个分裂基因之间的相互作用）并非仅由box7元件介导。文中讨论了脱辅基细胞色素b内含子阅读框突变产物导致细胞色素c氧化酶亚基I基因转录本加工出现这些异常事件的可能性。
