J Biochem 1990 Sep 01;1083:347-55. doi: 10.1093/oxfordjournals.jbchem.a123205.

Sea urchin protease specific to the SPKK motif in histone.

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A protease activity specific to spermatogenous histones was found in the egg extract of sea urchin. The enzyme responsible for this activity, named SPKK protease because of its substrate specificity, was purified as a monomeric 28 kDa protein. SPKK protease activity is inhibited by leupeptin and is specific to the repeat of sequences like Ser-Pro-Lys-Lys (the SPKK motif) [Suzuki, M. (1989), EMBO J. 8, 797-804]. The DNA-binding sites of sea urchin spermatogenous histones H1 and H2B, which protect the linker DNA of chromatin, are made up of sequences rich in the SPKK motif. SPKK protease may contribute not only to the unpacking of sperm chromatin but also to transcription activation of the male origin gene at fertilisation. SPKK protease resembles another protease activity on nucleolin [Burger et al. (1982) Eur. J. Biochem. 128 475-480] in its characteristics.

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Genes referenced: LOC100887844 LOC593162 LOC752081 LOC756768