CHARACTERIZATION OF AN A T-RICH FAMILY OF SEQUENCES FROM CHANNEL CATFISH (ICTALURUS-PUNCTATUS)/

A family of highly repetitive DNA sequences referred to as Xba element s was identified and characterized from the channel catfish (Ictalurus punctatus) genome. The Xba elements represent about 5% to 6% of the t otal genomic DNA of the channel catfish. The Xba elements are distribu ted specifically in the channel catfish and blue catfish (I. furcatus) , but not in closely related species such as white catfish (Ameiurus c atus) and flathead catfish (Pylodictus olivaris). These Xba elements a re ar-ranged-as head-to-tail tandem repeats. Seven sequences were sequ enced. They are A/T-rich (over 65%). Each sequence contains four copie s of the ATTA repeat and eight copies of (A)(3-6) GT/TG motifs whose f unction is not known. Each unit of the repeats is 325 bp from the Kans as strain, and 321 ph from the Auburn and Stuttgart strains of channel catfish. The Xba elements ate conserved in length within a specific s train, and highly conserved in sequence identity. Sequence identity is more conserved among copies isolated from the same strain than from d ifferent strains. The sequence length polymorphism among strains may b e useful for identification of strains by polymerase chain reaction an alysis. Many features of these elements could make them potentially im portant for development of homologous recombination expression vectors and position-independent expression vectors.