ABSTRACT: Since one of the two X chromosomes is randomly inactivated at an early stage of female embryonic development, X- linked markers have been used to study the origin and development of various neoplastic disorders in affected heterozygous women; clonality assays have provided a useful tool to the understanding of the mechanisms underlying the development of neoplasia. Recently, a technique of clonal analysis has been devised that takes advantage of a highly polymorphic short tandem repeat within the X-linked human androgen receptor (AR) gene, resulting in a heterozygosity rate approaching 90%. The rapid expansion of the number of women now suitable for X inactivation analysis has however given rise to new controversies, one of the more troublesome being the possibility of a modification of the pattern of X- chromosome inactivation pattern in blood cells of elderly women. In the present study we analyze with the AR assay a group of 166 healthy females aged between 8 and 94 years, with no history of genetic or neoplastic familial disorders. We failed to find any correlation between age and X- chromosome inactivation pattern ( r = 0.17), even subdividing the subjects in different age groups according to the criteria used by other researchers, and therefore reaffirm that, when tested for with well-standardized and accurate criteria, extremely unbalanced inactivation of the X chromosome is a truly uncommon phenomenon in normal women.

Keywords: X inactivation, skewing, androgen receptor.

Reprint requests to: Anna Maria Ferraris, M.D., Ematologia Oncologica, IST, Largo Rosanna Benzi,10,16132 Genova, ITALY, phone: 390105600933, fax: 39010509052, e-mail: gaetani@mbox.ulisse.it.

ABSTRACT: We present homology models of the C domains of coagulation factors V (FV) and VIII (FVIII). Using a threading approach, we identified the binding domain of galactose oxidase as an appropriate template for each C domain. The C1 and C2 domains of FV associate to form an elongated cylinder of 80Å long and 30Å diameter. The folding unit is a beta-sandwich with a long axis of 40Å and a diameter of 30Å. The current model allows us to propose a membrane binding mode for the C2 domains of FV and FVIII with three major characteristics: 1) solvent-exposed hydrophobic side chains from three loops at one end of the beta- sandwich are buried in the hydrophobic layer of the outer phospholipid leaflet; 2) a crown of positively charged residues is located in the polar zone of the phospholipid head groups; and 3) the long axis of the beta-sandwich of the C2 domain is perpendicular to the plane of the membrane. This proposal satisfies experimentally observed characteristics of membrane binding for the C2 domain and the light chain of FVa.

Keywords: Blood coagulation, factor V, factor VIII, phospholipid, thrombosis, membrane, modeling.

Reprint requests to: Elizabeth D. Getzoff, Ph.D., Department of Molecular Biology, The Scripps Research Institute, 10550 North Torrey Pines Road, La Jolla, CA 92037, phone: (619) 784-2878, fax: (619) 784-2277, e-mail: edg@scripps.edu.