Specificity of Mammalian Y-box Binding Protein p50 in Interaction with ss and ds DNA Analyzed with Generic Oligonucleotide Microchip

p50 protein is a member of the Y-box binding transcription factor family and is a counterpart of YB-1 protein. The generic microchip was used to analyze the sequence specificity of p50 binding to single (ss) and double-stranded (ds) oligodeoxyribonucleotides. The generic microchip contained 4096 single-stranded octadeoxyribonucleotides in which all possible core 6-mers (46=4096) were flanked at their 3′ and 5′-ends with degenerated nucleotides. The oligonucleotides were chemically immobilized within polyacrylamide gel pads fixed on a glass slide. The binding of p50 to the generic microchip was shown to be the most specific to ss GGGG motif and then to ss CACC and CATC motifs. GC-rich ds oligonucleotides of the generic microchip, and particularly those containing GGTG/CACC, GATG/CATC, and GTGG/CCAC heterogeneous motifs, were most efficiently destabilized due to interaction with p50. Gel-shift electrophoresis has shown that the protein exhibits much higher binding specificity to 24-mer oligoA-TGGGGG-oligoA containing G-rich 6-mer, in comparison with 24-mer oligoA-AAATAT-oligoA carrying A,T-rich 6-mer in full correspondence with the data obtained with the microchip. Studies of DNA-binding proteins using gel-immobilized ss and ds DNA fragments provide a unique possibility to detect low-affinity complexes of these proteins with short sequence motifs and assess the role of these motifs in sequence-specific interactions with long recognition sites.