| Metazoans display an extraordinarily broad spectrum of functional and behavioural complexity. The size of the proteome of an organism can be expanded during evolution by increasing the numbers of genes, by elaborating pre-existing mechanisms that generate protein diversity and/or by elaborating the relationships between components (for example, regulatory networks), and by inventing new mechanisms. Mechanisms that increase protein diversity in all metazoans include the use of multiple transcription start sites, alternative pre-mRNA splicing, polyadenylation, pre-mRNA editing, and post-transcriptional protein modification. Among these mechanisms, alternative Pre-mRNA splicing is considered to be the most important source of protein diversity in vertebrates. The recent completion of a draft of human genome indicated that alternative splicing of Pre-mRNAs plays a crucial role in obtaining biological complexity, because more than 59% of the human genes seem to be alternatively spliced (Hastings and Krainer 2001).In addition, it was estimated that about 15% of all mutations that cause a genetic disease in humans lead to a failure in the correct splicing of the corresponding pre-mRNA, which disturbs the expression of the gene (Philips and Cooper 2000). Thus, the removal of pre-mRNA introns plays a major role in gene regulation. As of 1999, around 100 splicing factors were identified; however (Burge et al., 1999), that number has now nearly doubled due primarily to improved purification of spliceosomes coupled with advances in mass spectrometry analyses of complex mixtures.Both genetic and biochemical studies have revealed that essential components of the spliceosome include five small RNAs-U1, U2, U4, U5 and U6, and as many as 300 distinct proteins. Here we reported the molecular cloning and functional analysis of a novel cDNA encoding for a protein of 149 amino acids. This protein has 38% amino acid sequence identity...
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