THE MOLECULAR BASIS FOR THE DIFFERENT DNA BINDING SPECIFICITIES OF CLASS I AND II PLANT TCP PROTEINS

RODRIGO RIPOLL; IVANA VIOLA; DANIEL GONZALEZ

Puerto Madryn

Congreso; XLVI Reunión Anual Sociedad Argentina de Investigación en Bioquímica y Biología Molecular; 2010

Sociedad Argentina de Investigación en Bioquímica y Biología Molecular

TCP genes encode plant-specific transcription factors with anoncanonical bHLH domain (the TCP domain) that allows DNAbinding and proteinprotein interactions. Based on sequencehomology, TCP proteins can be divided in two classes, I and II.SELEX experiments using rice proteins suggested that proteinsfrom each class have distinct DNA binding specificities(GTGGGNCC versus GTGGNCCC). To gain insight into the DNAbinding properties of class I TCP transcription factors, weperformed a SELEX experiment with the Arabidopsis class Iprotein TCP16, a divergent member of this class. This assayindicated that TCP16 prefers the class II-like sequenceGTGGNCCCGS. In an effort to understand this behavior, weconstructed site-specific mutants of TCP16, TCP20 (class I) andTCP4 (class II) in residues conserved inside each class andchimeras between the TCP domains of TCP4 and TCP20 andanalyzed their DNA binding properties. Altogether these assaysdemonstrated that the presence of Gly at position 11 of the TCPdomain of class I proteins and Asp11 in TCP16 and class II proteinsis responsible for the different DNA binding preferences of theseproteins. The results also showed that the presence of the class IHLHdomain confers higher DNA binding selectivity.