The Pxmp2 and PoleI genes are linked by a bidirectional promoter in an evolutionary conserved fashion.

Pxmp2 is the most abundant peroxisomal membrane protein in higher eukaryotes. Its expression is tissue-specific with highest levels of expression in liver, kidney and heart tissue. We have analysed the 5'-flanking genomic region of the murine Pxmp2 gene and we found, that the first exon of the gene encoding the DNA polymerase epsilon (PoleI) was localized adjacent to the first exon of the Pxmp2 gene in head to head orientation. Both genes were separated by only 393 bp containing a CpG island with numerous binding sites for Sp1. A TATA box, however, was lacking. Northern blot analysis revealed that both genes were expressed differently, indicating that their expression was regulated independently. We have analysed the promoter activity of the small genomic fragment separating the Pxmp2 and PoleI genes using luciferase as a reporter molecule in transient transfection assays. The small genomic fragment was a functional promoter, controlling gene expression regardless of its orientation. Promoter activity was 60-70% compared with the activity of the strong CMV promoter. The Pxmp2 and PoleI genes were also linked on the human and rat genome. Furthermore, the sequence of the intergenic fragment was highly conserved among these species. Thus, the small intergenic fragment is probably the common basic element of two independently regulated promoters.

Murine calmodulin binding protein 1 (Calmbp1): tissue-specific expression during development and in adult tissues.

Expression of the 1.9 kb cDNA of murine Calmbp1 has been shown to interfere with the mitotic S-M checkpoint in yeast (J. Cell Sci. 111 (1998) 3609). The physiological function and expression pattern of Calmbp1 in mice, however, are unknown. We have investigated the expression of Calmbp1 in mid-gestation and late-gestation fetuses and in adult organs of the mouse. In Northern blot analyses, using a Calmbp1-specific probe, a single mRNA of more than 7.4 kb was found that showed a progressive decline in total RNA preparations of fetal heads during the period from day E12 to E16. In the adult, this Calmbp1 transcript was detectable by Northern blot analysis exclusively in testis, ovary and spleen of all organs examined. In situ hybridizations revealed that Calmbp1 is expressed (a) in the differentiating central and peripheral nervous system, (b) in the epithelial cells lining the crypts of the small intestine in late gestation and adult mice, (c) in the fetal, but not the adult liver, (d) in both the fetal and adult spleen, where the signal colocalized with hematopoetic cells in the red pulp, (e) in late gestation embryos in the thymus, S-shaped tubules in the kidney, epidermis, and (f) in leptotene, zygotene and pachytene spermatocytes of the adult testis and the follicle epithelium of the activated follicles in the adult ovary.