L6, IL-TMP, and TM4SF5 are cell surface proteins
predicted to have four transmembrane domains. Previous
sequence analysis led to their assignment as members of
the tetraspanin superfamily. In this paper, we identify
a new sequence (L6D) that is strikingly similar to L6,
IL-TMP, and TM4SF5. Analyses of these four sequences indicate
that they are not significantly related to genuine tetraspanins,
but instead constitute their own L6 superfamily.