EPSTEIN-BARR-VIRUS RECOMBINANT MOLECULAR-GENETIC ANALYSIS OF THE LMP1AMINO-TERMINAL CYTOPLASMIC DOMAIN REVEALS A PROBABLE STRUCTURAL ROLE,WITH NO COMPONENT ESSENTIAL FOR PRIMARY B-LYMPHOCYTE GROWTH TRANSFORMATION

Previous recombinant Epstein-Barr virus molecular genetic experiments with specifically mutated LMP1 genes indicate that LMP1 is essential f or primary B-lymphocyte growth transformation and that the amino-termi nal cytoplasmic and first transmembrane domains are together an import ant mediator of transformation. EBV recombinants with specific deletio ns in the amino-terminal cytoplasmic domain have now been constructed and tested for the ability to growth transform primary B lymphocytes i nto lymphoblastoid cell lines. Surprisingly, deletion of DNA encoding EHDLER or GPPLSSS from the full LMP1 amino-terminal cytoplasmic domain (MEHDLERGPPGPRRPPRGPPLSSS) had no discernible effect on primary B-lym phocyte transformation. These two motifs distinguish the LMP1 amino-te rminal cytoplasmic domain from other arginine-rich membrane proximal s equences that anchor hydrophobic transmembrane domains, Two deletions which included the ERGPPGPRRPPR motif adversely affected but did not p revent transformation. This arginine- and proline-rich sequence is pro bably important in anchoring the first transmembrane domain in the pla sma membrane, since these mutated LMP1s had altered stability and cell membrane localization. The finding that overlapping deletions of the entire amino-terminal cytoplasmic domain do not ablate transformation is most consistent with a model postulating that the transmembrane and carboxyl-terminal cytoplasmic domains are the likely biochemical effe cters of transformation.