U7 snRNAs： A Computational Survey

U7 small nuclear RNA (snRNA) sequences have been described only for a handful of animal species in the past. Here we describe a computational search for func- tional U7 snRNA genes throughout vertebrates including the upstream sequence elements characteristic for snRNAs transcribed by polymerase Ⅱ. Based on the results of this search, we discuss the high variability of U7 snRNAs in both se- quence and structure, and report on an attempt to find U7 snRNA sequences in basal deuterostomes and non-drosophilids insect genomes based on a combination of sequence, structure, and promoter features. Due to the extremely short se- quence and the high variability in both sequence and structure, no unambiguous candidates were found. These results cast doubt on putative U7 homologs in even more distant organisms that are reported in the most recent release of the Rfam database.     

The head structure of a higher plant V-type H+-ATPase is not always a hexamer but also a pentamer

Pentameric head structures of the V-type H⁺–ATPase ofMesembryanthemum crystallinum L. were demonstrated in additionto hexameric head structures by rotational image analysis andmolecular projections of negatively stained H⁺–ATPaseheads. This observation, at least partially, is in contrastto the standard model of the V-type H⁺–ATPase predictingsolely a hexameric head structure with three A and three B subunitsin analogy to the F-type ATPases. With one A or B subunit missingtwo A or two B subunits would be adjacent to each other in thepentameric ATPase head. By chemical cross-linking of H ⁺–ATPasesubunits a crosslinking product exclusively consisting of Bsubunits, in addition to a cross-linking product consistingof subunits A and B was detected. Thus, the pentameric headsmight lack one A subunit, although the lack of one B subunitcan not be totally ruled out. We assume that the hexameric headstructure is the catalytically active configuration while thepentameric head structure may be a relatively stable intermediateof turnover. Key words: V-type H⁺–ATPase, protein structure, electron microscopy, tonoplast, Mesembryanthemum crystallinum L     

U7 snRNAs: A Computational Survey

U7 small nuclear RNA (snRNA) sequences have been described only for a handful of animal species in the past. Here we describe a computational search for func- tional U7 snRNA genes throughout vertebrates including the upstream sequence elements characteristic for snRNAs transcribed by polymerase Ⅱ. Based on the results of this search, we discuss the high variability of U7 snRNAs in both se- quence and structure, and report on an attempt to find U7 snRNA sequences in basal deuterostomes and non-drosophilids insect genomes based on a combination of sequence, structure, and promoter features. Due to the extremely short se- quence and the high variability in both sequence and structure, no unambiguous candidates were found. These results cast doubt on putative U7 homologs in even more distant organisms that are reported in the most recent release of the Rfam database.