SEQUENCE ELEMENTS SURROUNDING THE ACCEPTOR SITE SUPPRESS ALTERNATIVE SPLICING OF THE SARCO ENDOPLASMIC RETICULUM CA2+-ATPASE 2-GENE TRANSCRIPT/

Expression of the muscle-specific 2a isoform of the sarco/ endoplasmic reticulum Ca2+-ATPase (SERCA2) requires activation of an inefficient optional splice process at the 3' end of the primary gene transcript, The sequence elements required for this regulated splice event were st udied by modifying a minigene containing the 3' end of the SERCA2 gene , An important requirement appears to be a strong muscle-specific acce ptor site, as replacing it by a weak one prevented the induction of mu scle-type splicing during myogenic differentiation, The induction of m uscle-type splicing did not depend on positive cis-active sequences in the muscle-specific exon, On the other hand, replacement of a broad r egion around the acceptor site dramatically deregulated the expression pattern, as this modification strongly induced muscle-type splicing i n undifferentiated muscle cells and in fibroblasts. This cis-active re gion is also involved in the suppression of the neuronal type of splic ing. Furthermore selective replacement of the acceptor site as well as deletions or replacements in the muscle-specific exon induced muscle- type splicing to various extents in undifferentiated myogenic cells. T herefore sequence elements in the distal part of the optional intron a nd in the muscle-specific exon contribute to the suppression of muscle -specific SERCA2 splicing.