Hernando N, Bartkiewicz M, Collin-Osdoby P, Osdoby P, Baron R
Department of Cell Biology, Yale University School of Medicine, New Haven, CT 06510, USA.
Proc Natl Acad Sci U S A. 1995 Jun 20;92(13):6087-91. doi: 10.1073/pnas.92.13.6087.
We have identified a second isoform of the catalytic A subunit of the vacuolar H+ pump in chicken osteoclasts. In this isoform (A2) a 72-bp cassette replaces a 90-bp cassette present in the classical A1 isoform. The A1-specific cassette encodes a region of the protein that contains one of the three ATP-binding consensus sequences (the P-loop) identified in this polypeptide, as well as the pharmacologically relevant Cys254. In contrast, the A2-specific cassette does not contain any of these features. These two isoforms, which appear to be ubiquitously expressed, are encoded by a single gene and are generated by alternative splicing of two mutually exclusive exons. The alternative RNA processing involves the recognition of a single site, the boundary between the A2- and A1-specific exons, as either acceptor (in A1) or donor (in A2) splice site.
我们已在鸡破骨细胞中鉴定出液泡H⁺泵催化性A亚基的第二种同工型。在这种同工型（A2）中，一个72碱基对的盒式结构取代了经典A1同工型中存在的一个90碱基对的盒式结构。A1特异性盒式结构编码该蛋白质的一个区域，该区域包含此多肽中鉴定出的三个ATP结合共有序列之一（P环），以及药理学上相关的半胱氨酸254。相比之下，A2特异性盒式结构不包含这些特征中的任何一个。这两种同工型似乎在各处均有表达，由单个基因编码，并通过两个相互排斥的外显子的可变剪接产生。可变RNA加工涉及识别单个位点，即A2和A1特异性外显子之间的边界，将其识别为剪接受体（在A1中）或供体（在A2中）剪接位点。
