- Email: [email protected]
Organization of ribosomal spacer sequences in Triturus
G e n o m i c Structure and Function in D e v e l o p m e n t ( 5 5 - 7 5 )
55 ORGANIZATION OF RIBOSOMAL SPACER SEQUENCES IN TRITURUS. F. Andronico, !. Nardi* and S. De L u c c h i n i * . Ist.Embr. Mol., CNR NapolJ; * I s t . I s t o l . e d Embri,Universit~ di Pisa, I t a l y . The ribosomal RNA genes of T r i t u r u s v u l g a r i s m e r i d i o n a l i s are c l u s t e r e d at v a r i a b l e and often m u l t i p l e chromosomal s i t e s . The rDNA repeats show only a l i m i t e d and d i s c r e t e size heterogeneity, and d i f f e r e n t c l u s t e r s from d i s t a n t genomic regions can share the same class of repeats. We have analyzed a genomic clone from T. v u l g a r i s m e r i d i o n a l i s contain!ng the NTS region which is responsible f o r the observed d i f f e r e n c e s in the repeat s i z e s . This region, close to the 3'-end of the 28s sequence, appears to be conserved among d i f f e r e n t T r i t u r u s species. Suggestively, part of the cloned sequence h y b r i d i z e s also to non-ribosomal DNA on genomic b l o t s of T . v u l g a r i s m e r i d i o n a l i s , and to specif i c chromosome l o c i which share with the t r u e ribosomal +s i t e s the p o s i t i v e react i o n to the Ag method.
56 SIGNIFICANCE OF TYPICAL "LANDMARK" LOOPS OF AMPHIBIAN LAMPBRUSH CHROMOSOMES : THE GLOBULAR LOOPS. N. Anselier, M.L. Bonnanfant-Jais, E. N'Da and M. Penrad-Moba~ed. Centre de Cytologic Exp6rimentale, CNRS, 67, rue Maurice GOnsbourg, 94200 Ivrysur-Seine, France. In amphibian lampbrush chromosomes, some lateral loops such as the globular loops, exhibit a characteristic morphology of their RNP matrix. We study the relationship between the typical morphology of these loops and their activity. Data obtained by LM and TEM both on ultrathin sections and on molecular spreads, as well as by SEM show that the morphology of their matrix is accounted for by an extreme compaction of the transcription products.From inhibition experiments using actinomycin D as well as from labeling experiments followed by autoradiogra phy,we conclude that this compaction corresponds to a storage of RNP products. Furthermore, since a specific morphology of the matrix is not always present in globular loops, we suggest that the storage could be followed by a release of the RNP products. We propose that the typical morpholop~y of the globular loops is caused by a cyclic transcriptional activi ty with storage and releasing periods.
27S
55 ORGANIZATION OF RIBOSOMAL SPACER SEQUENCES IN TRITURUS. F. Andronico, !. Nardi* and S. De L u c c h i n i * . Ist.Embr. Mol., CNR NapolJ; * I s t . I s t o l . e d Embri,Universit~ di Pisa, I t a l y . The ribosomal RNA genes of T r i t u r u s v u l g a r i s m e r i d i o n a l i s are c l u s t e r e d at v a r i a b l e and often m u l t i p l e chromosomal s i t e s . The rDNA repeats show only a l i m i t e d and d i s c r e t e size heterogeneity, and d i f f e r e n t c l u s t e r s from d i s t a n t genomic regions can share the same class of repeats. We have analyzed a genomic clone from T. v u l g a r i s m e r i d i o n a l i s contain!ng the NTS region which is responsible f o r the observed d i f f e r e n c e s in the repeat s i z e s . This region, close to the 3'-end of the 28s sequence, appears to be conserved among d i f f e r e n t T r i t u r u s species. Suggestively, part of the cloned sequence h y b r i d i z e s also to non-ribosomal DNA on genomic b l o t s of T . v u l g a r i s m e r i d i o n a l i s , and to specif i c chromosome l o c i which share with the t r u e ribosomal +s i t e s the p o s i t i v e react i o n to the Ag method.
56 SIGNIFICANCE OF TYPICAL "LANDMARK" LOOPS OF AMPHIBIAN LAMPBRUSH CHROMOSOMES : THE GLOBULAR LOOPS. N. Anselier, M.L. Bonnanfant-Jais, E. N'Da and M. Penrad-Moba~ed. Centre de Cytologic Exp6rimentale, CNRS, 67, rue Maurice GOnsbourg, 94200 Ivrysur-Seine, France. In amphibian lampbrush chromosomes, some lateral loops such as the globular loops, exhibit a characteristic morphology of their RNP matrix. We study the relationship between the typical morphology of these loops and their activity. Data obtained by LM and TEM both on ultrathin sections and on molecular spreads, as well as by SEM show that the morphology of their matrix is accounted for by an extreme compaction of the transcription products.From inhibition experiments using actinomycin D as well as from labeling experiments followed by autoradiogra phy,we conclude that this compaction corresponds to a storage of RNP products. Furthermore, since a specific morphology of the matrix is not always present in globular loops, we suggest that the storage could be followed by a release of the RNP products. We propose that the typical morpholop~y of the globular loops is caused by a cyclic transcriptional activi ty with storage and releasing periods.
27S