Proceedings of the Japan Academy, Series B

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We have developed a novel procedure to analyze highly repetitive and transcribable (Hirt) sequences present in animal cells, that is, total DNA transcription in vitro. Total DNAs from various animals were transcribed in vitro in a HeLa cell extract and it was found that one to several discrete RNAs were transcribed by RNA polymerase III. We determined the highly repetitive and transcribable sequences in calf, tortoise, newt and salmon detected by total DNA transcription and demonstrated that 5' parts of these four Hirt sequences have close resemblance to specific tRNA genes. In the cases of tortoise (Geoclemys reevessi) and newt (Cynops pyrrhogaster), the 5' parts of these sequences appear to have been derived from a lysine tRNA₁, (rabbit) gene (78% homology) and a glutamic acid tRNA (Drosophila) gene (74% homology) (not counting the aminoacyl stem region), respectively. The homologies extended to secondary structures, homologous nucleotides being located on similar secondary structures. The idea is proposed that many, if not all, highly repetitive and transcribable (Hirt) sequences detected by total DNA transcription have their own specific tRNA genes as their progenitors.

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Karyotypes of two Japanese insectivorous species, Crocidura dsinezumi chisai (2n=40, FN=52) and C. horsfieldi watasei (2n=26, FN=48), are investigated by G- and C-banding pattern analysis. Based on the G-banding patterns it is suggested that the 7 meta- or submetacentric pairs observed in C. h. watasei have been developed by the Robertsonian fusion of 10 acrocentric pairs, and also the centromere-telomere translocations between two subtelocentric and acrocentric pairs included in the C. d. chisai karyotype.

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The behavior of the B-chromosomes in the first spermatocytes of two Japanese raccoon dogs, which are observed previously in the spermatogonial cells, is described in the present paper. The B's in the most first spermatocytes are conjugated end-to-end, but some ones remained as the univalent condition. Thus, most of the first spermatocytes have at least one bivalent or trivalent of B's.

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The numerical distribution of B-chromosomes in the second spermatocytes of the Japanese raccoon dogs is described in this paper. Most of the second spermatocytes had one or two B's. The number of B's in the second spermatocytes well coincides with the expected one calculated from the meiosis-I. The wide distribution of the B's in the wild population of this animal is considered to be due to the conjugation of B's in the meiotic-I.

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