Deletion of chromosome 13q14 is the most frequent genetic aberration in B-cell chronic lymphocytic leukemia (CLL), found in more than 50% of cases, indicating that this region contains a gene(s) involved in the development of CLL. However, the pathogenic gene in the critical 13q14 region has not yet been de¢ned. Here, we have cloned and characterized a novel gene, DLEU7, located adjacent to the consensus deleted region, and overlapping the 3P P end of DLEU1 tail to tail. Human DLEU7 encodes a putative 221 amino acid protein, with signi¢cant conservation in rodents. Mutational and expression analysis in primary CLL samples failed to demonstrate any speci¢c mutations in DLEU7, but no DLEU7 expression could be detected in CLL cells. Methylation of a CpG island in the promoter region of DLEU7 was further analyzed as a possible mechanism for the absence of DLEU7 expression, and the promoter was found to be methylated in the majority of the CLL samples investigated.

Rapid progress in the sequencing of the genome of man and other species allows for the comparative analysis of their genetic structure and content. We have used a combined biochemical and computer-based approach to characterize a 146 kb human genomic bacterial artificial chromosome clone from chromosome 5q13 and discovered a novel human elongation-factor gene, hEFG2. The complete human EFG2 cDNA sequence is 3033 bp and contains 21 exons with conserved exon-intron splice junctions encompassing 45 kb of the genomic sequence with its 5'-end residing within a CpG island, characteristic of a housekeeping gene. The complete size of the hEFG2 cDNA was confirmed by Northern blot and reverse transcription/polymerase chain reaction analysis, which showed a single transcript of 3.2 kb ubiquitously expressed in various human tissues. The hEFG2 protein shows significant homology to several bacterial EF-G proteins, including that of Thermus thermophilus, and to the yeast Saccharomyces cerevisiae mitochondrial elongation factor-G ( MEF2). Multiple alignments reveal a novel gene family of mitochondrial EF-G proteins that can by divided into two subgroups, EF-G1 and EF-G2, in several eukaryotic species including S. pombe, Caenorhabditis elegans and Drosophila melanogaster. Using the information contained in the public databases, we also identified and cloned the complete coding sequence of the human EFG1 gene on chromosome 3q25. The cloning and characterization of these human mitochondrial elongation factor genes should permit us to address their role in the regulation of normal mitochondrial function and in various disease states.

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Our group previously identified two novel genes, RFP2/LEU5 and DLEU2, within a 13q14.3 genomic region of loss seen in various malignancies. However, no specific inactivating mutations were found in these or other genes in the vicinity of the deletion, suggesting that a nonclassical tumor-suppressor mechanism may be involved. Here, we present data showing that the DLEU2 gene encodes a putative noncoding antisense RNA, with one exon directly overlapping the first exon of the RFP2/LEU5 gene in the opposite orientation. In addition, the RFP2/LEU5 transcript can be alternatively spliced to produce either several monocistronic transcripts or a putative bicistronic transcript encoding two separate open-reading frames, adding to the complexity of the locus. The finding that these gene structures are conserved in the mouse, including the putative bicistronic RFP2/LEU5 transcript as well as the antisense relationship with DLEU2, further underlines the significance of this unusual organization and suggests a biological function for DLEU2 in the regulation of RFP2/LEU5.

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