Abstract
A new member, hARF4, of the ADP-ribosylation factor (ARF) family, a subset of the superfamily of regulatory GTP-binding proteins, has been cloned from a cDNA expression library. Two other human ARF cDNA sequences, designated human ARF1 and ARF3, have been reported previously and are 96% identical in amino acid sequence. A human ARF1 cDNA, significantly longer than previously described clones, was obtained, by cross-species hybridization using a bovine ARF1 cDNA probe. Bovine ARF1p and human ARF1p are 100% identical while each is only 80% identical to hARF4p. Thus, hARF4p is the most divergent of the mammalian ARF proteins identified. Northern blot analysis revealed the expression of at least three different ARF messages in human placenta and adrenal carcinoma cells. Both hARF1 and hARF4 encode GTP-binding proteins with predicted molecular masses of 20,000-21,000 Da. Biochemical analysis of the purified recombinant proteins revealed a high degree of conservation of nucleotide binding properties and in vitro ARF activities. ARF is an essential gene in the yeast, Saccharomyces cerevisiae, and is encoded by two genes. Expression of either hARF1p or hARF4p in yeast was found to rescue the lethal double mutant, arf1-arf2-, thus demonstrating the functional conservation of ARF functions between yeast and man. The combination of in vivo and in vitro assays for ARF function provides a specific and unambiguous means of determining bona fide ARF proteins from divergent species from among the rapidly increasing number of structurally related, small molecular weight GTP-binding proteins.
Highlights
A newmember,hARF4, of the ADP-ribosylation binding proteins which will be found expressed in factor (ARF) family, a subset of the superfamily of a single cell type or tissue will likely total between 30 and regulatoryGTP-bindingproteins,hasbeencloned
ADP-ribosylation factor (ARF) cDNA sequences, designated human ARFl and ysis, it is currently notpossible in many instances todiscrim
The human ARFl cDNA was cloned by hybridization of a radiolabeled bovine ARFl cDNA probe to a human foreskin fibroblast cDNA library [13]
Summary
Cloning of ARF cDNAs by hybridiprotein fractionation have allowed the identification of a zation with nucleotide probes has identified at least two ARF surprisingly large number of structurally related monomeric genes in cows (designated bARFl [8] and bARF2 [9]), man GTP-binding proteinswith molecular masses between 20 and (designated hARFl [10] and hARF3 ( l l ) ) , and yeast The two defined functions of ARF presumably involve distinct biochemical steps as well as cellular compartments, as no role for ADP-ribosylation has been described in the protein secretion pathway While these differences are not addressed directly in thispaper we have used these ARF activities to unambiguously define one functional subfamily of the GTP-binding proteins. Resultspresented in thispaper document for the first time that ARF proteins are well conserved both structurally and functionally in evolution, suggesting that the role of ARF is basic to cellular physiology and further genetic and biochemical studies inyeast will likely prove directly relevant to similar studies inman
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
