RIBOSOMAL HETEROGENEITY FROM CHROMATIN DIMINUTION IN ASCARIS-LUMBRICOIDES

The genome of Ascaris lumbricoides encodes both germline- and soma-spe cific proteins homologous to the eukaryotic small ribosomal protein (R p) S19. The two Ascaris homologs differ by 24 amino acid substitutions and are both components of the small ribosomal subunits. In oocytes, the germline RpS19 homolog (RpS19G) predominates. During chromatin dim inution, however, the gene is eliminated from all presomatic cells, an d RpS19G is replaced by the product of the somatic gene (RpS19S). Chro matin diminution in A. lumbricoides causes a change in the protein com position of ribosomes during development and represents an alternative means of gene regulation.