Identification of a cis-acting element involved in the regulation of BACE1 mRNA alternative splicing.

beta-site APP cleaving enzyme 1 (BACE1) is the transmembrane aspartyl protease that catalyzes the first cleavage step during proteolysis of the beta-amyloid precursor protein, a process involved in the pathogenesis of Alzheimer disease. BACE1 pre-mRNA undergoes complex alternative splicing, and cis-acting elements important for its regulation have not been identified. We constructed and compared several BACE1 minigenes and found that BACE1 sequence from exon 3 through exon 5 was required for minigenes to undergo correct splicing.

Promotion of BACE1 mRNA alternative splicing reduces amyloid beta-peptide production.

Production of the amyloid beta-peptide (Abeta) via sequential proteolytic cleavage of the amyloid precursor protein by beta- and gamma-secretases is strongly implicated in the pathogenesis of Alzheimer disease. The beta-secretase that executes the first cleavage event is a transmembrane aspartyl protease known as beta-site amyloid precursor protein-cleaving enzyme 1 (BACE1). BACE1 pre-mRNA is alternatively spliced through the use of alternative splice sites in exons 3 and 4, although the significance of these splicing events is unclear.

DNA replication of mitotic chromatin in Xenopus egg extracts.

Prereplication complexes are assembled at eukaryotic origins of DNA replication in the G1 phase of the cell cycle, and they are activated in S phase by cyclin-dependent kinase (Cdk)2/cyclin E and Cdk2/cyclin A. Previous experiments using Xenopus nuclear assembly egg extracts suggested that Cdk1/cyclin A, which is normally active in early mitosis, can replace the function of Cdk2 in driving DNA replication, whereas Cdk1/cyclin B, which functions later in mitosis, cannot. Here, we use a completely soluble replication system derived from Xenopus egg extracts to show that Cdk1/cyclin B also can support DNA replication.