Virtually all of our present understanding of repertoire development in c~/3 T-cells, particularly at the molecular level, has come from studies on humans and mice but there has been very little work done on other species (reviewed by Davis and Bjorkman 1988;Strominger 1989). In some instances, the use of alternative species, especially larger animals, would afford significant experimental advantages such as providing a longer time span over which to study fetal T-cell ontogeny, and also by allowing better access to lymphocytes recirculating through specific regions of the body, both in adult animals and in fetuses. However, the lack of sequence information for T-cell receptor (Tcr) segments and the unavailability of homologous probes has prevented a molecular analysis of the T-cell repertoire in these animals. We have begun to alleviate this in the case of sheep, an animal which offers both of the experimental advantages mentioned above, and have recently reported the basic molecular characterization of the sheep Tcr,, Tcr~ and Tcr~ chains (Hein et al. 1990(Hein et al. , 1991)). We have now analyzed a group of Tcrt~ chain cDNA clones derived from a postnatal thymus and from recirculating CD4 + T cells and in this communication report the sequences of a number of C, V, and J region segments.
Two cDNA libraries were screened during the present work. The methods used during library preparation and screening have been described in detail previously (Hein et al. 1989;Grossberger et al. 1990). The first library was prepared in the Xgtl 1 vector from RNA isolated from the thymus of a single eight-week-old lamb. A second library was constructed in the XZAP vector from RNA prepared from a pool of CD4 ÷ T cells that had been purified by panning from the efferent lymph of the prescapular nodes
The nucleotide sequences reported in this paper have been submitted to the GenBank database and have been assigned the accession numbers M94181-M94183.