During
infection of human parvovirus B19 (B19V), one viral
precursor mRNA (
pre-mRNA) is transcribed by a single promoter and is alternatively spliced and alternatively polyadenylated. Here, we identified a novel cis-acting sequence (5'-GUA AAG CUA CGG GAC GGU-3'), intronic splicing enhancer 3 (ISE3), which lies 72
nucleotides upstream of the second splice acceptor (A2-2) site of the second intron that defines the exon of the
mRNA encoding the 11-kDa
viral nonstructural protein. RNA binding motif
protein 45 (RBM45) specifically binds to ISE3 with high affinity (equilibrium dissociation constant [KD ] = 33 nM) mediated by its
RNA recognition domain and 2-homo-oligomer assembly domain (RRM2-HOA). Knockdown of RBM45 expression or ectopic overexpression of RRM2-HOA in human erythroid progenitor cells (EPCs) expanded ex vivo significantly decreased the level of viral
mRNA spliced at the A2-2 acceptor but not that of the
mRNA spliced at A2-1 that encodes VP2. Moreover, silent mutations of ISE3 in an infectious
DNA of B19V significantly reduced 11-kDa expression. Notably, RBM45 also specifically interacts in vitro with ISE2, which shares the octanucleotide (GGGACGGU) with ISE3. Taken together, our results suggest that RBM45, through binding to both ISE2 and ISE3, is an essential host factor for maturation of 11-kDa-encoding
mRNA.IMPORTANCE Human parvovirus B19 (B19V) is a human pathogen that causes severe hematological disorders in immunocompromised individuals. B19V
infection has a remarkable tropism with respect to human erythroid progenitor cells (EPCs) in human bone marrow and fetal liver. During B19V
infection, only one viral
precursor mRNA (
pre-mRNA) is transcribed by a single promoter of the viral genome and is alternatively spliced and alternatively polyadenylated, a process which plays a key role in expression of
viral proteins. Our studies revealed that a cellular
RNA binding protein, RBM45, binds to two intron splicing enhancers and is essential for the maturation of the small nonstructural
protein 11-kDa-encoding
mRNA. The 11-kDa
protein plays an important role not only in B19V
infection-induced apoptosis but also in
viral DNA replication. Thus, the identification of the RBM45
protein and its cognate binding site in B19V
pre-mRNA provides a novel target for
antiviral development to combat B19V
infection-caused severe hematological disorders.