TY  - JOUR
A1  - Sommerville, John
A1  - Scheer, Ulrich
T1  - Transcription of complementary repeat sequences in amphibian oocytes
N2  - Repeat sequences are transcribed in the germinal vesicles of amphibian oocytes. In the hnRNA population both complements of the repeats are found and can be readily detected because they form intermolecular duplex structures. The structure and formation of duplex regions have been studied in the hnRNA of Xenopus laevis, Triturus cristatus, Amphiuma means and Necturus maculosus, a series of amphibians of increasing genome size (C-value). In T. cristatus, the duplex structures are mostly 600- 1200 bp in length, whereas in X. laevis they are shorter and in N. maculosus they tend to be longer. Although the proportion of RNA sequence capable of rapidly forming duplex structures is different in different organisms, this property bears no relationship to C-value. However the sequence complexity of complementary repeats, as estimated from the rate of duplex formation, does show an increasing trend with C-value. The complementary repeats found in oocyte hnRNA are transcribed from families of DNA sequence that are each represented in the genome by thousands of copies. The extent of cross-species hybridization is low, indicating that the repeat sequences transcribed in different amphibian genera are not the same. In situ hybridization experiments indicate that the repeat sequences are spread throughout the genome. The evolution and possible function of complementary repeats are considered.
Y1  - 1982
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-33915
ER  - 
TY  - JOUR
A1  - Scheer, Ulrich
A1  - Sommerville, John
T1  - Sizes of chromosome loops and hnRNA molecules in oocytes of amphibia of different genome sizes
N2  - The lengths of lampbrush chromosome loops and their tran scription units show a positive correlation with genome size in oocytes of amphibia with different C values. However, there is no such correlation with contour lengths of hnRNA molecu les isolated from these oocytes. These results indi cate th at more ON A sequences are transcribed in amphibia of higher C value , but that processing of RNA transc ripts occurs while they are still attached to the chromosomes as nascent ribonucleoprotein fibrils.
Y1  - 1982
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-33094
ER  -