The TAp63 isoform has been shown to be pro-apoptotic and can bind to p53 response elements, driving transcription of p53 target genes. The DNp63 isoform, however, acts as a dominant-negative competitor for TAp63 and p53. The DNp63 isoform is expressed at higher levels than TAp63 during development and at lower levels during differentiation. Consequently, it has been suggested that the ratio of DNp63 to TAp63 isoform expression may dictate whether a cell follows its normal differentiation program, becomes senescent, or undergoes oncogenic transformation. It is, therefore, not surprising that DNp63 is the predominant isoform expressed in human breast cancers. Interestingly, DNp63 has been shown to interact with and regulate the Wnt signaling pathway, promoting cell proliferation. Thus, Wnt signaling through Lrp5 may regulate the proliferative potential of the basal mammary stem cell population by inhibiting senescence. We conclude that profound differences in regenerative potential are not necessarily reflected at the gross level of epithelial organogenesis. Instead, there are changes in the predisposition of the Yunaconitine cellular populations to senescence, and perhaps to growth stimuli and transforming events. The diversity and organization of cellulases and other proteins involved in plant cell wall breakdown by rumen cellulolytic bacteria is fundamental to understanding how ruminants extract energy from their diet. The cellulolytic enzyme system from R. flavefaciens FD-1 has been shown to include a variety of exo-b-1,4-glucanases, endo-b-1,4-glucanases and cellodextrinases. Difficulties were encountered in initial fractionation of these enzymes as they appeared to exist in high-molecular-weight protein complexes resembling cellulosomes, and enzymatic activity was lost rapidly when the complexes were disrupted. Individual bglucanase genes were cloned from R. flavefaciens FD-1 with a view to studying their regulation. Meanwhile, parallel studies in the related R. flavefaciens strain 17 also led to the sequence analysis of a number of xylanases and cellulases. This revealed the presence of multiple catalytic modules in xylanases and the presence of noncatalytic dockerins and of substrate-binding modules in both cellulases and xylanases. The hypothesis that these Chloroquine Phosphate dockerincontaining enzymes are organized into cellulosomes was supported by the discovery of the sca cluster of genes in R. flavefaciens 17 that encodes the cohesin-containing scaffolding or anchoring proteins ScaA, B, C and E. Evidence was obtained in R. flavefaciens 17 that many enzymes are assembled into the cellulosome complex via cohesin-dockerin interactions involving the ScaA “scaffoldin” protein, while other, currently unknown, proteins appear to be accommodated via the ScaC adaptor protein. ScaA in turn binds via its C-terminal dockerin to ScaB, which is held into the cell surface via another cohesin-dockerin interaction with the cell-wall anchored protein ScaE. The homologous sca cluster has now been identified in R. flavefaciens FD-1 and shows close alignment in gene order with that in R. flavefaciens 17, although interesting interstrain differences exist in the modular structures of ScaA and ScaB. Experimental verification of specific cohesindockerin interactions indicates that a broadly similar cellulosome organization exists in R. flavefaciens FD-1 and 17. Genes encoding several molecular chaperones have also been described from R. flavefaciens FD-1 that could be involved in the assembly of cellulosome-like structures. Genome sequencing of R. flavefaciens FD-1 offers the prospect of obtaining far more extensive information.