Sequence,Genomic Organization,and Expression of the Human ADP-Ribosylation Factor 6 ( ARF6 ) Gene: A Class III ARF

ADP-ribosylation factor 6 (ARF6) is a member of a family of ∼20-kDa guanine nucleotide-binding proteins that has been implicated to function in membrane ruffling and cell motility, endocytosis, exocytosis, and membrane recycling. Sequence analysis of the human ARF6 gene indicates it spans 4004 bp, contains a single 98-bp intron within the 5′-untranslated region, and is localized to chromosome 14q21. Similar to the class II ARF transcripts, translation of the ARF6 mRNA initiates in the second exon. Primer extension assays indicate that the major transcription initiation site is located 591 bp 5′ to the start of translation, yielding the largest 5′-untranslated region of the known human ARFs. The proximal 5′-flanking region of the human ARF6 gene lacks a TATA box and is highly GC rich. Consistent with this promoter structure, expression analysis of a blot containing 50 human RNAs hybridized with an ARF6-specific oligonucleotide probe revealed that the ARF6 gene is expressed in all tissues; although higher levels of expression were observed in heart, substantia nigra, and kidney. A comparison of the genomic organization of the ARF genes reveals that the ARF6 gene (class III) structure is quite distinct from the class I (ARF1, ARF2, and ARF3) and class II (ARF4 and ARF5) ARF genes.