Relationship between the major protein kinase C substrates acidic 80‐kDa protein‐kinase‐C substrate (80K) and myristoylated alanine‐rich C‐kinase substrate (MARCKS)

Two major protein‐kinase‐C (PKC) substrates have been described in the literature; an 87‐kDa bovine and human PKC substrate, called MARCKS, and an acidic 80‐kDa PKC substrate, isolated from rat brain and Swiss 3T3 cells, termed 80K. Since there is only 66–74% sequence similarity between MARCKS and 80K, we have further investigated their relationship in this study. Southern‐blot experiments with gene‐specific probes demonstrated the presence of the 80K, but not MARCKS, gene in the mouse genome. Furthermore, polymerase‐chain‐reaction (PCR) analyses using three pairs of primers that specifically recognise either 80K, MARCKS or conserved sequences of both genes, revealed the presence of only the 80K gene in the mouse and rat genomes and only the MARCKS gene in the bovine and human genomes with mRNA expression in the corresponding brain tissues. Northern‐blot analysis of a variety of tissues indicated that both 80K and MARCKS have similar patterns of expression. Most components of signal‐transduction pathways are present in multiple molecular isoforms as members of a gene family. In contrast, the findings presented in this study indicate that rodent 80K and bovine and human MARCKS are not distinct members of a gene family, but represent the equivalent substrates in different species.