Schäfer B, Wolf K
Institut für Biologie IV (Mikrobiologie) der Rheinisch-Westfälischen Technischen Hochschule Aachen, Worringer Weg, D-52056 Aachen, Germany.
Curr Genet. 1999 Jul;35(6):602-8. doi: 10.1007/s002940050458.
We describe herein a large group-II intron which is inserted in the mitochondrial cox1 gene of the Schizosaccharomyces pombe strain EF2. The intron RNA consists of 2492 nucleotides which can be folded into a secondary structure with all the expected sequence motifs of subgroup-IIA1 introns (Michel et al. 1989). Determination of the exact splice point revealed that the intron is inserted in the same codon, but 1 bp downstream, as the mobile intron aI2 in the Saccharomyces cerevisiae cox1 homologue. A total of nine nucleotide changes was observed around the insertion site of the intron in the cox1 gene of strain EF2 compared with the reference strain ade7-50h(-). Seven of these changes are clustered within the 51 bp upstream of the splice point. Only one sequence deviation was found in the downstream exon. The intron is capable of splicing despite the fact that both the EBS1/IBS1 and the EBS2/IBS2 sequence motifs, thought to be necessary for correct splicing, extend over 5 instead of 6 bp. The maturase, endonuclease and reverse transcriptase domains of the putative protein encoded by the newly described S. pombe group-II intron were not closer to those encoded by the other two, cobI and cox2I, S. pombe group-II introns than to the group-II intron-encoded proteins in Allomyces, Marchantia, Podospora and Saccharomyces.
我们在此描述了一个大的II组内含子，它插入到粟酒裂殖酵母菌株EF2的线粒体cox1基因中。该内含子RNA由2492个核苷酸组成，可折叠成具有IIA1亚组内含子所有预期序列基序的二级结构（Michel等人，1989年）。精确剪接位点的确定表明，该内含子插入的密码子与酿酒酵母cox1同源物中的移动内含子aI2相同，但在下游1个碱基处。与参考菌株ade7-50h(-)相比，在菌株EF2的cox1基因内含子插入位点周围共观察到9个核苷酸变化。其中7个变化聚集在剪接位点上游的51个碱基内。在下游外显子中仅发现一个序列偏差。尽管EBS1/IBS1和EBS2/IBS2序列基序（被认为是正确剪接所必需的）延伸了5个而不是6个碱基，但该内含子仍能够进行剪接。新描述的粟酒裂殖酵母II组内含子编码的推定蛋白质的成熟酶、内切核酸酶和逆转录酶结构域，与另外两个粟酒裂殖酵母II组内含子（cobI和cox2I）编码的结构域相比，与异水霉、地钱、柄孢壳菌和酿酒酵母中II组内含子编码的蛋白质结构域的亲缘关系并不更近。
