One of the major unresolved questions in cancer biology is why the majority of tumour cells express mutant p53 proteins. p53 is considered the prototype tumour suppressor protein, whose inactivation is the most frequent single genetic event in human cancer (Bourdon et al., 2005). Genetically-engineered p53-null knockout mice acquire multiple tumours very early on in life and human Li-Fraumeni families who carry germline mutations in p53 are highly cancer-prone (reviewed in Vousden and Lane, 2007). p53 mutant proteins have been found to acquire novel functions that promote cancer cell proliferation and survival, yet exactly why mutant p53s acquire oncogenic activity is still poorly understood. Mutant p53 has also been found to complex with wildtype p53, thus acting in a dominant negative way. However, this inhibition is incomplete since many cancers with mutant p53 alleles also have a loss of the second wild-type p53 allele and thus only express the mutant p53 (Baker et al., 1989). An N-terminal truncated p53 isoform, p47, arising from alternative splicing of the p53 gene (Ghosh et al., 2004) or by alternative initiation sites for translation (Yin et al. , 2002), has been described. Alternative splicing was found to be universal in all human multi-exon genes (Wang et al., 2008) and therefore determining the role of the p47 isoform with respect to the p53 gene is essential. Evidence in this study suggests that mutant p53 (p53RI75H) has a similar structure and function as p47, including the ability to complex with and impair both p53 and p73. Therefore, in addition to expressing a tumour suppressor protein, the p53 gene can also express an onco-protein (p47). This study therefore argues that tumours select for mutant p53 because it has gained the ability to function like p47, a wild-type p53 isoform.

No description available.

Mechanisms of post-transcriptional control are critical to deploy RNAs and proteins asymmetrically to a discrete region of cytoplasm at the posterior of the Drosophila oocyte and embryo, called the pole plasm and thus allow differentiation of the germline. Research presented in this thesis investigates the post-transcriptional control of Drosophila pole plasm component germ cell-less (gcl ). Maternal gcl activity is required for germ cell specification and gcl RNA and protein accumulate asymmetrically in the pole plasm. gcl RNA, but not Gcl protein, is also detected in somatic regions of the embryo, and ectopic expression of Gcl in the soma causes repression of somatic patterning genes suggesting that gcl RNA is subject to translational control. I find that Gcl is expressed during oogenesis, where its expression is regulated by translational repressor Bruno (Bru). Increased levels of Gcl are observed in the oocyte when Bru is reduced (i.e., in an arrest heterozygote) and Bru overexpression reduces the amount of Gcl. Consistent with this, reduction of the maternal dosage of Bru leads to ectopic Gcl expression in the embryo, which, in turn, causes repression of anterior huckebein RNA expression. Bruno binds directly to the gcl3'UTR in vitro, but surprisingly, this binding is largely independent of a Bruno Response Element (BRE) in the gcl 3'UTR and depends upon a novel site. Furthermore, the gcl BRE-like region is not required to repress Gcl expression during oogenesis or embryogenesis. I concluded that Bru regulates gcl translation in a BRE-independent manner. In addition, I established the role of the gcl 3'UTR in gcl RNA localization and translation using transgenes that replace the endogenous 3'UTR with the alpha-tubulin 3'UTR or place it in tandem to the bicoid 3'UTR. I find that accumulation of gcl RNA in the embryonic pole plasm requires the gcl 3'UTR. Moreover, Gel is restricted to the pole plasm by translational repression mediated by the gcl 3'UTR and a limiting pool of trans-acting translational repressors. The phenotypic consequences of loss of this translational control are relatively mild, suggesting that gcl translation does not require stringent repression in the soma.

No description available.

The nuclear lamina protein, lamin A is produced by proteolytic cleavage of a 74 kDa precursor protein, prelamin A. The conversion of this precursor to mature lamin A is mediated by a specific endoprotease, prelamin A endoprotease. Subnuclear fractionation indicates that the prelamin A endoprotease is localized at the nuclear membrane. The enzyme appears to be an integral membrane protein, as it can only be removed from the nuclear envelope with detergent. It is effectively solubilized by the detergent n-octyl-beta-D-glucopyranoside and can be partially-purified (approximately 1200-fold) by size exclusion and cation exchange (Mono S) chromatography. Prelamin A endoprotease from HeLa cells was eluted from Mono S with 0.3 M sodium chloride as a single peak of activity. SDS-PAGE analysis of this prelamin A endoprotease preparation shows that it contains one major polypeptide at 65 kDa and smaller amounts of a second 68 kDa polypeptide. Inhibition of the enzyme activity in this preparation by specific serine protease inhibitors is consistent with the enzyme being a serine protease.