Surf5:A Gene in the Tightly Clustered Mouse Surfeit Locus Is Highly Conserved and Transcribed Divergently from therpL7A(Surf3) Gene

The four previously characterized genes (Surf1to4) of the mouse Surfeit locus do not share any sequence homology, and the transcription of each gene alternates with respect to its neighbor(s). Adjacent Surfeit genes are separated by very small distances, and two of the genes overlap at their 3′ ends. In this work we have further defined the Surfeit gene cluster by the isolation ofSurf5,a fifth gene of the locus, and determination of its relationship to the other Surfeit genes.Surf5does not share any sequence homology with the four cloned Surfeit genes. The transcription ofSurf5is divergent with respect to its neighbor theSurf3gene, and the 5′ ends ofSurf5andSurf3are separated by only 159 bp, suggesting the presence of a second bidirectional promoter in the locus. The 3′ end ofSurf5maps only 68 bp away from the processed 3′ end of a pseudogene. The human and partial chickenSurf5coding regions show greater than 95% identity, and aCaenorhabditis eleganshomologue shows 38% identity and 56% similarity with the mouseSurf5amino acid sequence. The 3.5-kb transcript ofSurf5encodes a small hydrophilic protein of 140 amino acid residues, which differs from the ribosomal protein L7a encoded by theSurf3gene or the integral membrane protein encoded by theSurf4gene. Subcellular fractionation located theSurf5protein to the soluble fraction of the cytoplasm. The Surfeit locus appears to represent a novel type of gene cluster in which the genes are unrelated by sequence or function; however, their organization may play a role in their gene expression.