CIS-ELEMENTS REQUIRED FOR HIGH-LEVEL EXPRESSION OF UNSPLICED GAG-CONTAINING MESSAGE IN MOLONEY MURINE LEUKEMIA-VIRUS

The 441-nucleotide (nt) region (nt 5325 to 5766) around the splice acc eptor (SA) site (nt 5491) was found to be necessary for high-level exp ression of gag-containing unspliced RNA of Moloney murine leukemia vir us (hl, Oshima, T. Odawara, T. Matano, H. Sakahira, K. Kuchino, A. Iwa moto, and H. Yoshikura, J. Virol, 70:2286-2295, 1996), Detailed geneti c dissection of the il ll-nt region revealed that the 5'-end 64 nt (nt 5325 to 5389) were necessary for high-level expression of the unsplic ed RNA when the spliced RNA was not produced, while the 3'-side 301 nt (nt 5466 to 5766) containing the SA site were necessary for producing spliced RNA. When the spliced RNA was produced, the unspliced RNA cou ld be expressed at a high level even when the 5'-end 64 nt were absent . Probably the virus sequence ensuring the splicing could produce an R NA structure able to compensate for the function of the 5'-end 64-nt r egion responsible for the expression of the unspliced RNA.