42S p48--the most abundant protein in previtellogenic Xenopus oocytes--resembles elongation factor 1 alpha structurally and functionally.

We have undertaken an immunological and biochemical analysis of the most abundant soluble protein of previtellogenic Xenopus oocytes, 42S p48. We show that this protein shares immunological cross-reactivity with elongation factor 1 alpha (EF-1 alpha). Direct assays of both 42S fractions and purified 42S p48 show that this cross-reactivity is of functional significance since 42S p48, like EF-1 alpha, can transfer charged amino acids to ribosomes. We further demonstrate that 42S p48 is degraded soon after the onset of vitellogenesis, while the EF-1 alpha concentration remains essentially unchanged during this transition. These properties of 42S p48 are discussed with regard to its role in oogenesis.