P1 Element Research Articles

Asymmetric replication in vitro from a human sequence element is dependent on adeno-associated virus Rep protein.

The DNA of human parvovirus adeno-associated virus type 2 (AAV) integrates preferentially into a defined region of human chromosome 19. Southern blots of genomic DNA from latently infected cell lines revealed that the provirus was not simply inserted into the cellular DNA. Both the proviral and adjoining cellular DNA organization indicated that integration occurred by a complex, coordinated process involving limited DNA replication and rearrangements. However, the mechanism for targeted integration has remained obscure. The two larger nonstructural proteins (Rep68 and Rep78) of AAV bind to a sequence element that is present in both the integration locus (P1) and the AAV inverted terminal repeat. This binding may be important for targeted integration. To investigate the mechanism of targeted integration, we tested the cloned integration site subfragment in a cell-free replication assay in the presence or absence of recombinant Rep proteins. Extensive, asymmetric replication of linear or open-circular template DNA was dependent on the presence of P1 sequence and Rep protein. The activities of Rep on the cloned P1 element are analogous to activities on the AAV inverted terminal repeat. Replication apparently initiates from a 3'-OH generated by the sequence-specific nicking activity of Rep. This results in a covalent attachment between Rep and the 5'-thymidine of the nick. The complexity of proviral structures can be explained by the participation of limited DNA replication facilitated by Rep during integration.

On a BPX-preconditioner for P1 elements

We derive an optimal multilevel preconditioner for nonconforming P1 element discretizations of second order elliptic boundary value problems.

Simple C0 approximations for the computation of incompressible flows

We study various regularization procedures accomodating the P1-P1 and Q1-Q1 discretization of the 2D Stokes problem. The results are, in the P1-P1 case, compared with those obtained with a simple stable P1 element, namely the Mini element. It is shown that the use of the latter is in fact equivalent to a regularization method. Finally, the practical importance of consistency is discussed and a new formulation is proposed to enforce that condition even in the P1-P1 case.

Hyperfine Fields at Nonmagnetic Atoms on Various Sites in Ferromagnetic Heusler Alloys

AbstractThe hyperfine fields at Fe and Sn, as determined by Mössbauer effect and NMR, in a new Heusler alloy Ru2FeSn, are reported. By comparison with corresponding data in rhodium based Heusler alloys, it is inferred that a preferential R–Sn (R = Ru or Rh) disorder exists in these alloys. The hyperfine field data on Rh atoms occupying different sites in rhodium Heusler alloys helps to narrow the range of the parameter incorporated to account for the preasymptotic behaviour in the Blandin‐Campbell model of the conduction electron polarization. The calculations indicate for the elements of the s–p series occupying D site in traditional Heusler alloys that, if the change in sign of the hyperfine field occurs at the s2–p2 element (the hyperfine fields at s2–p1 and s2–p3 elements on D site being always observed to be negative and positive, respectively), then for s–p elements on (A, C) site, the change in sign will occur at the s2–p1 element and on B site, it will occur at the s2–p2 element but with the phase reversed i.e., the field at s2–p1 and s2–p3 is positive and negative, respectively. These predictions find strong support from recent experimental data in Heusler alloys.