Transcriptional Activity of Long Terminal Repeat and Cellular Flanking Regions of Intracisternal A-Particle Gene 81

Abstract

The intracisternal A-type particles (IAPs) are defective endogenous retroviral-like entities encoded by a family of proviral elements in the mouse genome. Our earlier studies demonstrated that IAP gene 81 was bounded by long terminal repeat sequences at both 5' and 3' ends. Furthermore, the cellular flanking regions of IAP gene 81 contain 16 pairs of potential z-DNA forming dinucleotide tract and several tandemly repeating dinucleotide tracts. To elucidate the functional roles of these sequences in affecting the expression of DNA regions in which the LAP gene was inserted, various constructs were made in which long terminal repeat or the cellular flanking z-DNA regions of IAP gene 81 were linked to a bacterial reporter gene, chloramphenicol acetyltransferase (CAT) gene. They were then transfected into various cell lines such as, NIH 3T3, HeLa and nasopharyngeal carcinoma cells. Results obtained showed that the putative z-DNA element in either sense or antisense orientation led to a relatively low level of constitutive CAT expression in the three cell limes. On the other hand, in HeLa and NIH 3T3 cells, long terminal repeat element in sense orientation elicited relatively significant promoter activity in the transient assays. It is suggesed that sequences flanking the IAP gene 81 body may not contribute to the high activity of IAP gene 81 expression. It is noteworthy that the z-DNA element present in the cellular flanking regions of IAP gene 81 may be the site preferred for the insertion.