Prothymosin alpha.
Prothymosin alpha (ProT alpha) is a highly acidic protein widely distributed in mammalian cells. Since its discovery in 1984, the biological role of this protein has been controversial. Initially, ProT alpha was considered a thymic factor with a hormonal-like role in the maturation of T-lymphocytes. However, molecular and cellular analyses led to conclude that ProT alpha is a nuclear protein required in proliferation events while failing to show a clear immunological effect. The involvement of ProT alpha in changes in the compaction state of chromatin has been recently elucidated with the demonstration that this protein induces the unfolding of chromatin fibres in a process that seems to be mediated by the interaction of ProT alpha with histone H1. This finding opens up new perspectives in the study of the dynamics of the genetic material in mammalian cells. Furthermore, the relationship between ProT alpha and apoptosis as well as with proliferation makes this protein an attractive target in the search for modulators of cell death and tumour growth.