Nuclease S1-sensitive sites in multigene families: human U2 small nuclear RNA genes.

We show here that human U2 small nuclear RNA genes contain a 'strong nuclease S1 cleavage site' (SNS1 site), a sequence that is very sensitive to digestion by nuclease S1. This site is located 0.50-0.65 kb downstream of the U2 RNA coding region. It comprises a 0.15-kb region in which (dC-dT)n:(dA-dG)n co-polymeric stretches represent greater than 90% of the sequence. Nuclease S1 is able to excise unit length repeats of the human U2 RNA genes both from cloned fragments and total human genomic DNA. The precise locations of the cleavage sites are dependent on the superhelicity of the substrate DNA. In negatively supercoiled substrates, cleavages are distributed over the entire 0.15-kb region, but in linearized substrates, they occur within a more limited region, mainly at the boundary of the SNS1 site closest to the human U2 RNA coding region. Nuclease S1 cleavage of negatively supercoiled substrates occurs at pHs as high as 7.0; in contrast, cleavage of linearized substrates requires a pH less than 5.0, indicating that supercoiling contributes to the sensitivity of this site. Mung bean nuclease gives results similar to that observed with nuclease S1.     

Deletion of an rRNA gene set in Bacillus subtilis

One of the 10 rRNA gene sets found in a wild-type strain of Bacillus subtilis 168 was deleted, apparently by recombination between two tandemly repeated rRNA gene sets. The deletion strain grew as well as the wild-type strain under a variety of growth conditions and also showed no change in the sporulation efficiency.     

The complete nucleotide sequence of the I-E alpha d immune response gene.

We have isolated and sequenced the complete murine I-E alpha immune response gene of the H-2db haplotype. The I-E alpha d gene consists of 5300 basepairs and is organized into five or possibly six exons that correspond to different domains of the alpha chain. The amino acid sequence deduced from the I-E alpha gene shows 75% homology to its human counterpart, the HLA-DR alpha chain. The absence of I-E antigen in H-2 mice is due to lack of E alpha chain synthesis. We show here that this defect is caused by a deletion in the 5' end of the I-E alpha b gene.     

Histocompatibility Gene Organization and Mixed Lymphocyte Reaction

TRANSFORMATION of allogenic lymphocytes in mixed cultures depends chiefly on an incompatibility between the lymphocyte donors at the major histocompatibility locus in man (HL-A), mouse (H-2) and rat (H-l)¹. Although the mouse H-2 locus can be divided into several regions each of which controls one or more antigenic specificities² and two or more subloci control HL-A antigens in man³, it is not known whether all parts of the major histocompatibility locus are equally important in eliciting transformation in mixed lymphocyte cultures. We now show that capacity to elicit lymphocyte transformation is different for different parts of the mouse H-2 locus.     

Isolation and analysis of (Gp)nXp sequences of rat liver 5S RNA by means of restricted ribonuclease T2 hydrolysis

Essentual difficulties arise when base number in oligoguanylic blocks and location of these blocks along the polynucleotide chain need to be determined in the course of determination of the nucleotide sequences in ribonucleic acids. To overcome this difficulty it is suggested to take advantage of a recently discovered resistance of phosphodiester bond between kethoxalated G and its 3′-neighbour against T₂ RNase hydrolysis 1,2. The approach is illustrated by analysis of 5S RNA from rat liver. Sequences of general formula (Gp)_nXp were isolated from T₂ RNase hydrolysate of 5 S RNA rapidly and quantitatively. The information obtained greatly facilitates the whole procedure of sequencing. It is expected that the method proposed would be effective for analysis of 5 S and 4 S RNA and for highmolecular weight fragments of ribosomal and viral RNAs.