Utilization of an 86 bp exon generates a novel adducin isoform (beta 4) lacking the MARCKS homology domain.
A novel isoform of beta-adducin has been amplified and characterized from a human bone marrow cDNA library (GenBank #U43959). This isoform arises from the insertion of an 86 bp alternatively spliced and previously unrecognized exon (now termed exon 15) within codon 581 of the human red blood cell beta-adducin sequence. This results in an insertion of 28 novel amino acids. The remainder of the red cell beta-adducin mRNA is then translated in a different reading frame, adding an additional 35 novel amino acids prior to the stop codon. This new isoform, thus, replaces beta 1-adducin sequence after residue 580 with a total of 63 new amino acids. Sequences from genomic clones of the human beta-adducin gene show that this alternate exon is flanked by splice consensus sequences and is appropriately located in the genomic map between exons encoding up-stream and down-stream sequences, thus defining a new exon. The COOH-terminus of this new isoform, which we designate beta 4, lacks a 22 amino acid lysine-rich sequence common to both the human red cell alpha- and beta-adducin subunits and homologous to a highly conserved region in MARCKS, a filamentous actin-cross linking protein regulated by protein kinase C and calcium/calmodulin. beta 4-adducin preserves a previously identified calmodulin binding domain. PCR analysis indicates that this new beta-adducin isoform is expressed in fetal brain and liver, bone marrow, and NT-2 (neuroepithelial) cells, but is not detected in several other tissues. We anticipate that this new beta 4 isoform of beta-adducin will display unique and tissue-specific functional properties.
Sinard
J H
JH
Department of Pathology, Yale University School of Medicine, New Haven, CT 06510, USA.
Stewart
G W
GW
Stabach
P R
PR
Argent
A C
AC
Gilligan
D M
DM
Morrow
J S
JS
D017398:Alternative Splicing; D000595:Amino Acid Sequence; D001483:Base Sequence; D002148:Calmodulin-Binding Proteins / Q000235:genetics*; D003001:Cloning, Molecular; D005091:Exons / Q000235:genetics*; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins; D007536:Isomerism; D008565:Membrane Proteins; D008969:Molecular Sequence Data; D000076250:Myristoylated Alanine-Rich C Kinase Substrate; D009928:Organ Specificity / Q000235:genetics; D016133:Polymerase Chain Reaction; D017434:Protein Structure, Tertiary; D011506:Proteins / Q000235:genetics*; D017386:Sequence Homology, Amino Acid; D012689:Sequence Homology, Nucleic Acid; D014158:Transcription, Genetic; D000099291:Adducins
D002148:Calmodulin-Binding Proteins; D047908:Intracellular Signaling Peptides and Proteins; D008565:Membrane Proteins; D000076250:Myristoylated Alanine-Rich C Kinase Substrate; D011506:Proteins; D000099291:Adducins; C000619710:MARCKS protein, human