Identification of two homologous cytochrome b5s in rat brain

Two kinds of PCR products were isolated from adult rat brain. The smaller product matched up to liver b5 mRNA completely. However, the larger one contained an additional 58 bp inserted between amino acids 96 and 97. This insertion was previously unknown and corresponded to in-frame codons for his-ser-ala-leu and the early stop. It is assumed that these two forms arise from a primary transcript by differential mRNA processing. This finding strongly suggests that there are two homologous b5s expressed in rat brain.