The mouse thymosin beta 4 gene: structure, promoter identification, and chromosome localization.

Thymosin beta 4 (T beta 4) is an actin monomer sequestering protein that may have a critical role in modulating the dynamics of actin polymerization and depolymerization in nonmuscle cells. Its regulatory role is consistent with the many examples of transcriptional regulation of T beta 4 and of tissue-specific expression. Furthermore, lymphocytes have a unique T beta 4 transcript relative to the ubiquitous transcript found in many other tissues and cells. To determine how T beta 4 gene expression is regulated and how the alternative transcripts are derived, we cloned the mouse T beta 4 gene. We established that there is a single mouse T beta 4 gene and found that the lymphoid-specific transcript is generated by extending the ubiquitous exon 1 with an alternate downstream splice site. The transcription start site is defined by primer extension analysis, and the 5'-flanking region has many of the characteristics of a promoter. It is pyrimidine-rich and contains typical promoter elements, including a GC box, an initiator site, and consensus transcription factor binding sites. The mouse T beta 4 gene locus (Ptmb4) is located by interspecific backcross mapping to the distal region of the mouse X chromosome, linked to Btk and Gja6.