Precursor of the major egg-yolk proteins that are sources of nutrients during early development of oviparous organisms. Produced by the liver, secreted into the blood and then sequestered by receptor mediated endocytosis into growing oocytes, where it is generally cleaved, giving rise to the respective yolk components. By steroids (estrogen). The serine-rich portion of vitellogenin encodes phosvitin (or two phosvettes). It is assumed to be phosphorylated to a level of about 80%.