cDNA clones coding for the endoplasmic reticulum Ca2+-transport ATPase have been cloned from a pig smooth-muscle cDNA library. The transcripts can be divided into two classes which differ in their 3′ ends due to alternative splicing of the primary gene transcript. The class 1 cDNA encodes a protein of 997 amino acids (Mr 110,000). The class 2 protein (1042 amino acids; Mr 115,000) is completely identical to the class 1 protein except that the four C-terminal amino acids of the class 1 protein are replaced in the class 2 protein with a tail of 49 amino acids. Comparison of these sequences with other Ca2+ pump sequences reveals that the class 1 isoform corresponds to the sarcoplasmic reticulum Ca2+ pump of slow-twitch skeletal/cardiac muscle, whereas the class 2 protein corresponds to a Ca2+ pump recently detected in non-muscle tissues.
Evidence for two isoforms of the endoplasmic-reticulum Ca2+ pump in pig smooth muscle
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J A Eggermont, F Wuytack, S De Jaegere, L Nelles, R Casteels; Evidence for two isoforms of the endoplasmic-reticulum Ca2+ pump in pig smooth muscle. Biochem J 15 June 1989; 260 (3): 757–761. doi: https://doi.org/10.1042/bj2600757
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