Genomic structure of HTLV (human T-cell leukemia virus): detection of defective genome and its amplification in MT-2 cells.

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Abstract
We studied the genomic structure of human T‐cell leukemia virus (HTLV) in the HTLV producer cell line MT‐2. Southern blotting revealed that at least eight HTLV proviruses were integrated in the chromosomes of MT‐2 cells. The genomic structure of these proviruses was analyzed using fragments of cloned HTLV that were specific to gag, pol, env, pXs and U3R genes as probes. We have identified a complete genome of HTLV in MT‐2 (non‐defective type). However, seven of the eight proviruses had defective genomes. Provirus T2‐a contains only the U3R (LTR) of HTLV and T2‐b corresponds to the non‐defective genome. T2‐c possesses only a portion of env, and pXs and U3R. T2‐d consists of gag, pol, part of env and U3R. On the other hand, T2‐e, f, g and h consist of gag, pXs and U3R. Northern blotting experiments with mRNA from MT‐2 cells supported the evidence of amplification of the gag‐pXs gene of HTLV. 26S mRNA is considered to be a subgenomic species of 35S RNA. 32S mRNA may represent the T2‐d provirus which lacks a portion of env and pXs, while 20S mRNA was a subgenomic species. The gag‐pXs gene may correspond to 24S mRNA, the amount which was amplified in MT‐2 cells.