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Cloning and characterization of the human ADP-ribosylation factor 4 gene
1University of Arkansas for Medical Sciences, Department of Biochemistry and Molecular Biology, Little Rock 72205, USA.
Abstract:
ADP-ribosylation factor 4 (ARF4) is a member of a family of approximately 20 kDa guanine nucleotide-binding proteins that were initially identified by their ability to stimulate the ADP-ribosyltransferase activity of cholera toxin in vitro. They have recently been shown to play a role in vesicular trafficking and as activators of phospholipase D. The organization of the human ARF4 gene was determined from a genomic clone isolated from an arrayed PAC genomic library. The gene spans approximately 12 kb and contains six exons and five introns. Translation initiates in exon 1 and terminates in exon 6. Nuclease protection experiments indicated that the major transcription initiation site is located 211 bp 5' to the start of translation. In some cell lines derived from human tissues, however, multiple initiation sites were observed. The proximal 5'-flanking region of the human ARF4 gene lacks a TATA box, is highly GC rich, and contains multiple potential Spl-binding sites. An alignment of the exons for the class I ARF genes (ARF1, ARF2, and ARF3) and class II ARF genes (ARF4 and ARF5) reveals that the members of each class share a common gene organization. The structures of the class I and II ARF genes, however, are quite distinct and support the division of the ARFs into these groups based on deduced amino acid sequence, protein size, phylogenetic analysis, and gene structure.
Insights
The human ADP-ribosylation factor 4 (ARF4) gene structure was analyzed, revealing six exons and five introns. Its regulatory region lacks a TATA box, indicating unique transcriptional control mechanisms for this vesicular trafficking protein.
Area of Science:
- Molecular Biology
- Genetics
Background:
- ADP-ribosylation factors (ARFs) are small GTP-binding proteins involved in vesicular transport.
- ARF4 plays a role in vesicular trafficking and activates phospholipase D.
- Understanding ARF gene organization provides insights into protein family evolution.
Purpose of the Study:
- To determine the genomic organization of the human ARF4 gene.
- To analyze the 5'-flanking region and transcriptional initiation sites of ARF4.
- To compare the gene structure of ARF4 with other ARF gene classes.
Main Methods:
- Genomic clone isolation from a PAC library.
- Nuclease protection experiments for transcription start site mapping.
- Sequence alignment of ARF gene families.
Main Results:
- The human ARF4 gene spans approximately 12 kb with six exons and five introns.
- The 5'-flanking region is GC-rich, lacks a TATA box, and contains Spl-binding sites.
- ARF4 and ARF5 (Class II) share a common gene organization distinct from ARF1-3 (Class I).
Conclusions:
- The gene structure of ARF4 supports its classification into Class II ARFs.
- Distinct gene structures correlate with ARF protein sequence, size, and phylogenetic relationships.
- The findings contribute to understanding the evolutionary divergence of the ARF gene family.