Sarcoplasmic reticulum Ca2+ pump mRNA stability in cardiac and smooth muscle: role of poly A+ tail length

Transcripts of the sarco/endoplasmic reticulum Ca2+ pump SERCA2 are alternatively spliced to produce SERCA2a (expressed in left ventricular muscle (LVM)) and SERCA2b (in stomach smooth muscle (SSM)) mRNA that use different polyadenylation sequences. SERCA2 mRNA in LVM is more stable than in SSM. Here, we report that the SERCA2 poly A+ tail length in LVM (32 +/- 2 bases) is longer than in SSM (20 +/- 1). In the in vitro decay assays, the 3'-region mRNA of SERCA2a or SERCA2b is more stable when the poly A+ tail is longer. However, when the poly A+ tail length is similar for SERCA2a and SERCA2b, the SERCA2a RNA is more stable. Thus, the longer poly A+ tail may contribute to, but does not appear to be the sole determinant of, greater stability of SERCA2 mRNA in LVM than in SSM.