Terry P. Moynihan

The Ubiquitin-conjugating Enzymes UbcH7 and UbcH8 Interact with RING Finger/IBR Motif-containing Domains of HHARI and H7-AP1

Ubiquitinylation of proteins appears to be mediated by the specific interplay between ubiquitin-conjugating enzymes (E2s) and ubiquitin-protein ligases (E3s). However, cognate E3s and/or substrate proteins have been identified for only a few E2s. To identify proteins that can interact with the human E2 UbcH7, a yeast two-hybrid screen was performed. Two proteins were identified and termed human homologue of Drosophila ariadne (HHARI) and UbcH7-associated protein (H7-AP1). Both proteins, which are widely expressed, are characterized by the presence of RING finger and in between RING fingers (IBR) domains. No other overt structural similarity was observed between the two proteins. In vitrobinding studies revealed that an N-terminal RING finger motif (HHARI) and the IBR domain (HHARI and H7-AP1) are involved in the interaction of these proteins with UbcH7. Furthermore, binding of these two proteins to UbcH7 is specific insofar that both HHARI and H7-AP1 can bind to the closely related E2, UbcH8, but not to the unrelated E2s UbcH5 and UbcH1. Although it is not clear at present whether HHARI and H7-AP1 serve, for instance, as substrates for UbcH7 or represent proteins with E3 activity, our data suggests that a subset of RING finger/IBR proteins are functionally linked to the ubiquitin/proteasome pathway.

Molecular analysis of the presenilin 1 (S182) gene in "sporadic" cases of Alzheimer's disease: identification and characterisation of unusual splice variants.

Abstract: Mutations of the presenilin 1 (PS‐1) gene at the Alzheimers disease (AD) FAD3 locus on chromosome 14q24.3 are responsible for the majority of familial early‐onset AD. As genes responsible for familial forms of AD are obvious candidates for further investigation in “sporadic” disease, we performed a molecular analysis of PS‐1 transcripts extracted from brain tissues of a series of histologically confirmed cases of “sporadic” AD (n = 10) and also from histologically “normal” (non‐Alzheimer) age‐matched brain controls (n = 5). No sequence changes in the PS‐1 coding sequence were detected after analysis by reverse transcription‐PCR. This suggests that the frequency of mutations in the PS‐1 (S182) coding region in “sporadic” Alzheimers disease is very low. However, we demonstrated that the PS‐1 gene is highly variably spliced. One splice variant involves the 5′ untranslated region of the PS‐1 gene only and hence encodes for normal PS‐1. Six further splice variants involve coding regions of the PS‐1 gene and result in truncated proteins lacking specific transmembrane domains. Most of these variants do not coincide with recognized sites of introns in the PS‐1 gene. One of these variants, resulting in the loss of transmembrane domain TM‐VII, was found only in an AD patient.

A human ubiquitin conjugating enzyme, L-UBC, maps in the Alzheimer's disease locus on chromosome 14q24.3.

We have identified a novel ubiquitin conjugating enzyme gene, L-UBC, which maps to human Chromosome (Chr) 14q24.3. This is also the location of the major early onset familial Alzheimers disease gene (FAD3). L-UBC encodes a protein that demonstrates homology to the yeast ubiquitin conjugating enzyme, UBC-4, and human UbcH5. Their functions are to ubiquitinate specific proteins targeted for degradation. The protein also exhibits very strong homology to a rabbit protein, E2-F1, which mediates p53 degradation driven by papilloma virus E6 protein in vitro. The accumulation of specific proteins that have undergone aberrant processing in neurofibrillary tangles and amyloid plaques is the classic pathological feature in brains of Alzheimers disease patients. Abnormal ubiquitination has previously been suggested to play a role in the etiology of Alzheimers disease. This gene therefore represents a plausible candidate gene for FAD3.

Rapid isolation of genomic clones for individual members of human multigene families : identification and localisation of UBE2L4, a novel member of a ubiquitin conjugating enzyme dispersed gene family

We describe a rapid, PCR-based, screening procedure for the isolation of human genomic clones in lambda bacteriophage, containing sequences coding for individual homologous members of a multigene family. The approach is based upon the identification, by dilution, of sub-pools of the genomic library that contain members of the gene family, prior to phage isolation. The presence of specific genes is established by PCR of aliquots of individually amplified library pools, using consensus primers and subsequent sequencing. We have used the approach to isolate a fourth member of the UBE2L gene family, UBE2L4, and located it on chromosome 19q13.1-->q13.2. This PCR-based approach to library screening has wider applicability in that it could be used to isolate alternate-spliced products from cDNA libraries.

Assignment1 of the ubiquitin conjugating enzyme gene, UBE2G2, to human chromosome band 21q22.3 by in situ hybridization

The yeast ubiquitin-conjugating enzyme, Ubc7, is involved in the degradation of mutant or misfolded membrane proteins (Biederer et al., 1996; 1997; Jungmann et al., 1993). We have now cloned the gene for the human homologue of yeast Ubc7, UBE2G2. A genomic DNA clone was obtained containing the 3)-end of this gene and used for fluorescence in situ hybridisation (FISH) to map the gene to chromosome 21q22. Screening of the Genebridge 4 radiation hybrid DNA panel also indicated a chromosome location at 21q22.3→qter (21.07 cR from WI3679, LOD 13.0). UBE2G2 is transcribed in most tissues but at particularly high levels in skeletal muscle and heart. The mapping of this gene to the Down’s Syndrome locus implies that inappropriate protein ubiquitination may occur in trisomy 21.

CHARACTERIZATION OF THE MOUSE UBIQUITIN-CONJUGATING ENZYME GENE UBCM4

Abstract. The ubiquitination pathway targets not only normal (short-lived) intracellular eukaryotic proteins for degradation when appropriate, but also serves to eliminate mutant/misfolded proteins from the cell. An understanding of the molecular basis of the interaction between the ubiquitin-conjugating enzymes (E2s), ubiquitin protein ligases (E3s), and target proteins is essential to explain the process in normal cellular function and in disease. UbcM4 is the mouse ortholog of the human E2, UbcH7, which can participate in the in vitro degradation of many proteins including p53. We describe the characterization of the mouse UbcM4 gene and the identification of a UbcM4 pseudogene. Four UbcM4 transcripts of approximately 0.7, 1.5, 2.1, and 2.6 kb, observed on Northern blots, are differentiated by their utilization of alternative UbcM4 polyadenylation sites. A single alternative splice variant cDNA, termed UbcM4Δex2, was also identified. The polypeptide encoded by UbcM4Δex2 is incapable of forming an ubiquitin-thioester in contrast to UbcM4, despite retaining the key cysteine residue essential for ubiquitin thioester formation and the active site consensus sequence that defines the ubiquitin-conjugating enzyme class. These observations are of particular relevance for analysis of UbcM4 function in vivo as our studies indicate that the targeted deletion of the coding exon absent in UbcM4Δex2 would produce an inactive UbcM4 protein and presents an alternative to disruption of its transcriptional initiation site/promoter region. Furthermore, it suggests that a similar strategy may be applicable to disrupt the function of other ubiquitin-conjugating enzymes in vivo.