Gene expression in interspecific hybrids. II. RNA synthesis in the lethal cross Arbacia lixula male x Paracentrotus lividus female.

All types of RNA are actively synthesized by the lethal hybrid obtained by fertilizing the eggs of the sea urchin Paracentrotus lividus with the sperm of another sea urchin species, Arbacia lixula. DNA-like RNA and ribosomal RNA seem to be less stable in hybrids than in normal A. lixula and P. lividus embryos. Labeled RNA's from A. lixula and P. lividus were found to hybridize about 2.5 times as well with DNA of their own species as with DNA of the other species. RNA from the interspecific hybrid hybridized from 1.6 times to twice as well with A. lixula DNA as with P. lividus DNA, although the hybrid embryos were previously shown(5) to contain more DNA of maternal than of paternal type. Transcription of the paternal (foreign) genome seems therefore to be favored in some way in the interspecific hybrid.