Abstract
We investigated the ability of the U3 region of the long terminal repeats (LTR) of the Friend murine leukemia virus (Fr-MuLV) and Moloney murine leukemia virus (Mo-MuLV) to promote transcription in a variety of human cell lines. Our analysis reveals the presence of a transcriptional enhancer with specificity for erythroid cells in the U3 region of the Fr-MuLV. This constitutes the first example of an enhancer with such a property. Analysis of the Mo-MuLV enhancer suggests that it is active at least in erythroid and lymphoid cells and has thus a less restricted specificity than the Fr-MuLV enhancer. The different tissue specificities of the two enhancers correlate with the different tissue selectivities and pathogenic properties of the two viruses.