No abstract

In this work we show for the first time that the overproduced N-terminal fragment (residues 1^91) of ribosomal protein TL5 binds specifically to 5S rRNA and that the region of this fragment containing residues 80^91 is a necessity for its RNA-binding activity. The fragment of Escherichia coli 5S rRNA protected by TL5 against RNase A hydrolysis was isolated and sequenced. This 39 nucleotides fragment contains loop E and helices IV and V of 5S rRNA. The isolated RNA fragment forms stable complexes with TL5 and its N-terminal domain. Crystals of TL5 in complex with the RNA fragment diffracting to 2.75 A î resolution were obtained.z 1999 Federation of European Biochemical Societies.

A novel DSN-depletion method allows elimination of selected sequences from full-length-enriched cDNA libraries. Depleted cDNA can be applied for subsequent EST sequencing, expression cloning, and functional screening approaches. The method employs specific features of the kamchatka crab duplex-specific nuclease (DSN). This thermostable enzyme is specific for double-stranded (ds) DNA, and is thus used for selective degradation of ds DNA in complex nucleic acids. DSN depletion is performed prior to library cloning, and includes the following steps: target cDNA is mixed with excess driver DNA (representing fragments of the genes to be eliminated), denatured, and allowed to hybridize. During hybridization, driver molecules form hybrids with the target sequences, leading to their removal from the ss DNA fraction. Next, the ds DNA fraction is hydrolyzed by DSN, and the ss fraction is amplified using long-distance PCR. DSN depletion has been tested in model experiments.

Penelope-like elements (PLEs) represent a new class of retroelements identified in more than 80 species belonging to at least 10 animal phyla. Penelope isolated from Drosophila virilis is the only known transpositionally active representative of this class. Although the size and structure of the Penelope major transcript has been previously described in both D. virilis and D. melanogaster transgenic strains, the architecture of the Penelope regulatory region remains unknown. In order to determine the localization of presumptive Penelope promoter and enhancer-like elements, segments of the putative Penelope regulatory region were linked to a CAT reporter gene and introduced into D. melanogaster by P-element-mediated transformation. The results obtained using ELISA to measure CAT expression levels and RNA studies, including RT–PCR, suggest that the active Penelope transposon contains an internal promoter similar to the TATA-less promoters of LINEs. The results also suggest that some of the Penelope regulatory sequences control the preferential expression in the ovaries of the adult flies by enhancing expression in the ovary and reducing expression in the carcass. The possible significance of the intron within Penelope for the function and evolution of PLEs, and the effect of Penelope insertions on adjacent genes, are discussed.