Isolation of a 7S particle from Xenopus laevis oocytes: a 5S RNA-protein complex.

Previtellogenic oocytes of Xenopus laevis contain a free 5S RNA-protein complex sedimentating at 7 S. This particle consists of one molecule of 5S RNA and one 45,000-dalton protein. The protein of the 7S particle and the protein that is released in association with 5S RNA when the ribosome is treated with EDTA are unrelated. Because the 5S RNA accumulated by small oocytes in storage particles is incorporated into the ribosome later in oogenesis, we conclude that 5S RNA is succesively associated with two proteins during the life span of the oocyte.