Comparison of mRNA and protein levels of four members of the protein 4.1 family: the type II brain 4.1/4.1B/KIAA0987 is the most predominant member of the protein 4.1 family in rat brain.

The human gene for the fourth member of the protein 4.1 family, KIAA0987, was recently identified by comprehensive cDNA analysis. To further characterize the corresponding gene and its product in rats, we cloned and sequenced rat KIAA0987 cDNA. RNA blot analyses revealed that the rat KIAA0987 gene was abundantly expressed only in the brain, kidney, and testis. Although we have previously reported that the third member of the protein 4.1 family, the KIAA0338 gene product, is predominantly expressed in rat brain, and thus was named brain 4.1, quantitative RNA blot analyses indicated that KIAA0987 should be called something other than brain 4.1 because the level of KIAA0987 mRNA was found to be of the same order as that of KIAA0338 mRNA. Our quantitative immunoblot analysis showed that the most predominant member of the protein 4.1 family at the protein level was the product of the KIAA0987 gene, not that of the KIAA0338 gene. Taking these results together, we consider it reasonable to name the KIAA0338 and KIAA0987 gene products 'type I brain 4.1' and 'type II brain 4.1,' respectively, because these two products were found to be more prominently produced in rat brain than the other two members of the protein 4.1 family, erythroid 4.1 and 4.1G.