The Organisation of Genes for Transfer RNA and Ribosomal RNA in Amoebae and Plasmodia of Physarum polycephalum

Abstract

Using hybridization techniques, nuclei from amoebae and plasmodia of P. polycephalum were found to contain 275 genes each coding for 5.8-S, 19-S and 26-S rRNA, 685 genes for 5-S rRNA and 1050 genes for tRNA. Hybridization of these RNA species to both amoebal and plasmodial DNA fractionated on CsCl gradients reveal that the 5.8-S, 19-S and 26-S rRNA genes are located at a satellite position (.rho. = 1.714 g/cm3) with respect to the main band of DNA, whereas 4-S and 5-S RNA genes are located exclusively in the main band of DNA (.rho. = 1.702 g/cm3). This result was confirmed by demonstrating that only the 5.8-S, 19-S and 26-S rRNA species hybridize to purified plasmodial ribosomal DNA. The 19-S and 26-S rRNA genes of amoebae are located on extrachromosomal DNA molecules of a discrete size (MW = 38 .times. 106) with identical properties of plasmodial ribosomal DNA.