Genetic differences between the pancytosolic and perinuclear forms of murine mortalin

To determine the genetic relation between the pancytosolic (uniformly distributed in cytoplasm-p66mot-1) and the perinuclear (p66mot-2) mortalin proteins found in normal and immortal mouse cells, respectively, we initiated the present study using PCR cloning, sequencing, and single nucleotide primer extension analyses. The results indicate that the difference between mot-1 and mot-2 at 2 bp in the open reading frame does not arise by mutations in the immortalized cells. Intriguingly, both mot-1 and mot-2 sequences were detected in genomic DNA from normal (CMEF) and immortal (RS-4) cells derived from the CD1-ICR mouse strain. We extended the analyses to four other strains of mouse and detected both mot-1 and mot-2 sequences in genomic DNA from the Balb/c mouse also. Swiss and C57BL/6 mice exhibited only mot-2 and the C3H He mouse only mot-1. Southern analyses on a mouse strain that showed the presence of only mot-2 (Swiss) and one that showed both mot-1 and mot-2 (CD1-ICR) by PCR revealed that there are structural differences between mot-1 and mot-2 loci. Furthermore, there appears to be a correlation between frequency of spontaneous immortalization of cultured mouse fibroblasts and the mot loci present in the mouse strain from which they were derived.