Precursor of the egg-yolk proteins that are sources of nutrients during embryonic development (Probable). May play a role in cholesterol uptake. May be involved in thermotolerance (PubMed:24957743). Synthesized in Caenorhabditis only by 32 cells building the intestine of adult hermaphroditic individuals; they are cotranslationally secreted into the body cavity and subsequently taken up by the gonad. RNAi-mediated knockdown causes a reduction in the uptake of cholesterol analog dehydroergosterol (DHE). Simultaneous RNAi-mediated knockdown of zmp-2 prevents a reduction in survival upon heat stress.