POSTTRANSCRIPTIONAL CONTROL AND KINETIC CHARACTERIZATION OF PROLINE TRANSPORT IN GERMINATING CONIDIOSPORES OF ASPERGILLUS-NIDULANS

In the filamentous fungus Aspergillus nidulans, L-proline uptake is me diated by the product of the prnB gene which codes for a member of a f amily of amino acid transporters found both in pro- and eukaryotes, Re gulation of prnB gene expression has previously been studied in great detail at the molecular level. However, no studies have addressed poss ible post-transcriptional controls or the kinetic characterisation of the PrnB transporter. Here we develop a rapid and efficient method for direct uptake measurements of proline in germinating conidiospores of A, nidulans. We make use of this method and Northern blot analyses in parallel to study the regulation of PrnB expression both at the level of prnB message accumulation and at a post-transcriptional level. The se studies show that (i) pathway-specific and wide-domain regulatory s ystems, previously shown to control prnB gene expression in multicellu lar mycelia, also operate in unicellular conidia committed to germinat ion; and (ii) PrnB activity is regulated in response to the nitrogen s ource present in the medium and the level of internally accumulated pr oline or other amino acids. We also characterise kinetically the PrnB transporter and a secondary proline transport system. Our results open new possibilities for studies using unicellular conidiospores of fila mentous fungi and constitute a necessary first step for a subsequent s tructure-function analysis of the PrnB transporter.