The scid defect affects the final step of the immunoglobulin VDJ recombinase mechanism

Abelson murine leukemia virus-transformed precursor B lymphocytes from scid (severe combined immunodeficient) mice, like A-MuLV transformants from normal mice, actively rearrange segments of their Ig heavy chain variable region gene locus during growth in culture. Targeting of recombination to appropriate segments appears normal in these lines as evidenced by initial rearrangement of sequences from within the D and JH locus to form aberrant "DJH" rearrangements and secondary rearrangement of sequences from within the VH locus to the aberrant "DJH" intermediates. A detailed analysis of the joints in these rearrangements indicates that the VDJ recombinase in scid pre-B cells can correctly recognize heptamernonamer signal sequences and perform precise endonucleolytic scissions at these sequences. We propose that the scid defect involves the inability of scid precursor lymphocytes to join correctly the cleaved ends of the coding strands of variable region gene segments.     

Enzymatic resynthesis of the "reactive site" bond in the modified aprotinin derivatives [seco-15/16]aprotinin and [Di-seco-15/16,39/40]aprotinin

On incubation of [di-seco-15/16,39/40]aprotinin with human plasmin, porcine pancreatic kallikrein or bovine or porcine trypsin in neutral or slightly alkaline solutions [seco-39/40]aprotinin is slowly formed with enzymatic resynthesis of the reactive-site bond 15/16. With chymotrypsin, however, further degradation of [di-seco-15/16,39/40]aprotinin takes place without enzymatic resynthesis. The apparent rate constants for the synthesis of [seco-39/40]aprotinin with kallikrein and trypsin have been determined and indicate that the bond-forming reaction is 10-200-fold slower with [di-seco-15/16,39/40]aprotinin than with [seco-15/16]aprotinin. The newly formed [seco-39/40]aprotinin has similar kinetic constants for the complexation with its cognate enzymes as aprotinin, indicating that any distortion of the secondary binding region due to cleavage of the Arg39-Ala40 bond does not seriously influence binding and affinities.     

Structural homology between different archaebacterial DNA-dependent RNA polymerases analyzed by immunological comparison of their components

The archaebacterial DNA-dependent RNA polymerases have a complex structure containing eight or more components. Immunochemical analysis shows an extensive homology between the components of the enzymes of nine different species. Two enzyme subtypes can be distinguished: that of the thermoacidophilic and/or sulfur-metabolizing archaebacteria with the composition BACDEFGHIJ and that of the methanogenic plus halophilic archaebacteria with the composition ABB'C(D).... Components B and B' of the latter subtype probably evolved by the division of the large component B of the BACD... type enzyme. The existence of the two subtypes corroborates the division of the archaebacteria into two phylogenetic main branches.     

Structural variability in the genome of phage ?H of Halobacterium halobium

Summary The partially circularly permuted, terminally redundant structure of the DNA of phage H has been confirmed by a cleavage map for the restriction enzymes PstI, ClaI, BglII, HindIII, and, partially, BamHI.Six variants of phage H have been isolated from 71 single plaques. Their genomes differ by several insertions, a deletion, and an inversion of a DNA segment with a minimal length of 11 kb. The inversion occurs with high frequency in variants carrying at the flanks of the invertible DNA in verted repeats of a 1.8 kb DNA element which shares sequence homology with the DNA of H. halobium and may be involved in the extreme variability of its genome.     

The nucleotide sequence of Euglena cytoplasmic phenylalanine transfer RNA. Evidence for possible classifications of Euglena among the animal rather than the plant kingdom

The nucleotide sequence of cytoplasmic phenylalanine tRNA from Euglena gracilis has been elucidated using procedures described previously for the corresponding chloroplastic tRNA [Cell, 9, 717 (1976)]. The sequence is: pG-C-C-G-A-C-U-U-A-m(2)G-C-U-Cm-A-G-D-D-G-G-G-A-G-A-G-C-m(2)2G-psi-psi-A-G-A-Cm -U-Gm-A-A-Y-A-psi-C-U-A-A-A-G-m(7)G-U-C-*C-C-U-G-G-T-psi-C-G-m(1)A-U-C-C-C-G-G- G-A-G-psi-C-G-G-C-A-C-C-A. Like other tRNA Phes thus far sequenced, this tRNA has a chain length of 76 nucleotides. The sequence of E. gracilis cytoplasmic tRNA Phe is quite different (27 nucleotides out of 76 different) from that of the corresponding chloroplastic tRNA but is surprisingly similar (72 out of 76 nucleotides identical) to that of tRNA Phe from mammalian cytoplasm. This extent of sequence homology even exceeds that found between E. gracilis and wheat germ cytoplasmic tRNA Phe. These findings raise interesting questions on the evolution of tRNAs and the taxonomy of Euglena.     

The organization of the gene for the human cerebroside sulfate activator protein

The organization of 14 exons covering 97% of the cDNA sequence of human cerebroside sulfate activator protein precursor has been determined from two overlapping EMBL-4 human genomic clones extending over 17kb. All exons and exon/intron splice junctions and five introns were sequenced. Exon 8 consists of only 9 bp and is involved in alternative splicing which generates three different mRNAs of cerebroside sulfate activator precursor.     

Comparative Effects of Pollen and Seed Migration on the Cytonuclear Structure of Plant Populations. I. Maternal Cytoplasmic Inheritance

We explicitly solve and analyze a series of deterministic continent-island models to delimit the effects of pollen and seed migration on cytonuclear frequencies and disequilibria in random-mating, mixed-mating and self-fertilized populations. Given the critical assumption of maternal cytoplasmic inheritance, five major findings are (i) nonzero cytonuclear disequilibria will be maintained in the island population if and only if at least some migration occurs each generation through seeds with nonrandom cytonuclear associations; (ii) immigrant seeds with no cytonuclear disequilibria can strongly affect the genetic structure of the island population by generating significant and long-lasting transient associations; (iii) with all else being equal, substantially greater admixture disequilibria are generally found with higher rates of seed migration into, or higher levels of self-fertilization within, the island population (with the possible exception of the heterozygote disequilibrium); (iv) pollen migration can either enhance or reduce the cytonuclear disequilibria caused by seed migration, or that due to mixed-mating in the absence of seed migration, but the effect is usually small and appears primarily to make a noticeable difference in predominantly outcrossing populations; and (v) pollen migration alone cannot generate even transient disequilibria de novo in populations with completely random associations. This same basic behavior is exhibited as long as there is some random outcrossing in the island population. Self-fertilized populations represent a special case, however, in that they are necessarily closed to pollen migration, and nonzero disequilibria can be maintained even in the absence of seed migration. All of these general results hold whether the population is censused as adults or as seeds, but the ability to detect nonrandom cytonuclear associations can depend strongly on the life stage censused in populations with a significant level of random outcrossing. We suggest how these models might be used for the estimation of seed and pollen migration.     

On the dynamics of DNA in aqueous solution. Pulse radiolysis studies using the light scattering detection method

Summary The kinetics of DNA chain breakage in solution induced by 2 µs pulses of 15 MeV electrons were investigated by light scattering. On irradiating native calf thymus DNA at room temperature the decrease of light scattering intensity (LSI) - due to double strand ruptures - shows a fast decay with a half life _1/2 of about 30 ms as well as a slow decay with _1/2 of about 10 s. With increasing temperature (20–40° C) both the total degree of degradation and the fraction of the fast decay increase due to the facilitated melting of segments between two single strand breaks on alternate strands forming a double strand break. Above 40° C a third mode of LSI decay with _1/2 of 5–10 s arises, indicating detachment of relatively long segments.The total relative decrease of LSI after irradiation A, which can be taken as a measure of the degree of degradation, follows the square of the absorbed dose in the case of native DNA, whereas on irradiating denatured DNA A rises linearly with dose. The decay of LSI due to the degradation of denatured DNA is much faster than that of native DNA with _1/2 down to 150 µs, depending on the absorbed dose. The half lives are interpreted in terms of the separation of fragments by diffusion and of the melting of double strand segments between two single strand breaks.