Germ cells of various animals contain a determinant that is called the germ
plasm. In amphibians such as Xenopus laevis, the germ plasm is composed of
mitochondria and electron dense germinal granules that are embedded in a f
ibrillar matrix, previous reports indicated that one of the components of g
erminal granules was mitochondrial large and small ribosomal RNA (mtlrRNA a
nd mtsrRNA). Utilizing a modified procedure for electron microscopy in situ
hybridization, we investigated the distribution of these RNAs along with o
ther components of the germ plasm in Xenopus laevis embryos. We found, that
contrary to previous reports, the mtlrRNA and mtsrRNA were located in clos
e vicinity to the germinal granules but were not major constituents of gran
ules. The majority of the mtlrRNA and mtlsrRNAs was present inside the mito
chondria and in the germ plasm matrix.