Junctate is a newly identified integral ER/SR membrane calcium binding protein, 
which is an alternative splicing form of the same gene generating aspartyl 
beta-hydroxylase and junctin. Screening a mouse heart cDNA library using canine 
junctin cDNA as a probe yielded three complete mouse heart cDNAs. One of the 
cDNAs is homologous to the previously reported human junctate. The three mouse 
junctate proteins are composed of 270, 259, and 215 amino acids (we named them 
junctate-1, -2, and -3). The apparent molecular masses of the mouse junctates in 
SDS-PAGE were in the range between 40 and 53 kDa. Northern and Western blot 
analyses indicate that mouse junctates are expressed in heart, brain, spleen, 
lung, liver, kidney, and stomach, but not in skeletal muscle. The apparent 
molecular weights of junctates from heart and brain were somewhat different from 
those from the other tissues tested, suggesting that there are tissue-specific 
expression patterns of the different junctate isoforms. Immunohistochemical 
studies showed that junctates were expressed both in ventricular and atrial 
tissues. This is the first study that shows the presence of 3 distinct cardiac 
junctate isoforms expressed in various mammalian tissues.