A 33-kDa polypeptide with homology to the laminin receptor: component of translation machinery.

A 33-kDa polypeptide (termed p40), which shares an antigenic determinant with a laminin receptor and is under translational control, is believed to serve as a precursor to the receptor and to be related to the neoplastic state. The present study of subcellular localization of this protein shows it to be a cytoplasmic component not associated with the plasma membrane. Most of the cellular p40 was found to be associated with polyribosomes as well as with 40S to 60S cytoplasmic particles. Conditions that lead to polysome disruption also caused release of the polysomal form of p40 as smaller particles, and polysome reconstitution was accompanied by uptake of p40 into these structures. Because of the large abundance of this protein in the cells (six to eight copies per ribosome), it is unlikely that it represents a factor that associates with the 40S preinitiation complex. The p40-containing particles appear to represent a newly discovered structure involved in the process of polysome formation.