The selenoprotein phospholipid hydroperoxide glutathione
peroxidase (PHGPx) is present in at least
three different isoforms in testis: as a cytosolic, as a
mitochondrial, and as a nuclear protein. We have recently
shown that a sperm nucleus-specific glutathione
peroxidase (snGPx) is identical to the mitochondrial
and cytosolic forms of PHGPx apart from
its N-terminus. This arginine-rich N-terminus of snGPx, reminiscent of protamines, is encoded by an alternative
exon located in the first intron of the PHGPx gene and is responsible for nuclear localisation and chromatin binding of snGPx [Pfeifer et al., FASEB J.
15 (2001), pp. 1236-1238]. By using a combination of
techniques including selective cloning of mRNA 5'
ends, RT-PCR, and S1 analyses, we provide evidence
that the transcript encoding the nuclear form is generated
by transcription initiation at an alternative promoter
and not by alternative splicing. We show that
the major transcription start region is located at 12
to 14 upstream of the AUG translation initiation site
of the sperm nucleus-specific exon and lacks a TATA
box. Two minor TATA-less transcription initiation sites
are located at around -30 and -45. We have shown by
in situ hybridisation that snGPx expression in testis,
like protamine expression, is restricted to late stages
of spermatogenesis whereas PHGPx expression is
only found in spermatocytes and early spermatids.
These findings have to be taken into account when
studying either the differential regulation of PHGPx
and snGPx expression in testis or the impact of putative
mutations in snGPx on male fertility in man.
Biological Chemistry keeps you up-to-date with the latest advances in the molecular life sciences. The journal publishes Research Articles, Short Communications, Reviews and Minireviews. Areas include: general biochemistry/pathobiochemistry, structural biology, molecular and cellular biology, genetics and epigenetics, virology, molecular medicine, plant molecular biology/biochemistry and novel experimental methodologies.