V257 is the name of a mutation on the Y chromosome.
There will probably be significantly more information posted at the article named "E-V257". This article is only about the mutation. Before Trombetta et al. (2011) E1b1b1b was the name of the clade defined by E-M81.
There has been discussion about the exact position of V257 on the haploforum of the E-M35 project. See http://community.haplozone.net/index.php?topic=2434.0