High conservation of the serum response factor within Metazoa: cDNA from the sponge Geodia cydonium

A cDNA clone encoding the sequence-specific DNA binding protein, serum response factor (SRF), has been isolated and analysed from the marine sponge Geodia cydonium. The 1443 bp long cDNA comprises an open reading frame of 1149bp, from which an aa sequence with a Mr 42,149 can be deduced. Sequence comparisons revealed that the aa sequence shares high homology to human and Xenopus laevis SRFs. Like these vertebrate sequences also the sponge sequence displays the MADS-box motif present in the DNA-binding domain. The SRF, and also other transcription factors, such as ternary complex factors, recognizes the serum response element (CArG box) in promoter regions of a series of cellular immediate-early genes, whose expression is controlled by growth factors. A related CArG box sequence is present in sponge gene, encoding a receptor tyrosine kinase. Expression of SRF is strongly regulated by temperature stress; after incubation of the sponge at high temperature, the 1.6 kb transcript of SRF is downregulated. It is suggested that the SRF is involved in the transcriptional regulatory circuits, which control the response of the animal to altered environmental conditions.