DNA sequencing and complementation studies have determined the precise
location and nature of the A. nidulans sod^VICI mutation. The temperature sensitive mutation occurs within the coding region of the sod^VI C gene and causes an amino acid substitution close to the C - terminus of the corresponding α-COP protein. An αCOP: GFP fusion protein has been shown to be fully functional in A. nidulans. The GFPtagged protein illuminates putative Golgi equivalents close to the hyphal tip.
GFP constructs were used to investigate the effects of cytoskeletal disrupters and
brefeldin A on the endomembrane system of A. nidulans. The anti-microtubule agents benomyl and nocodazole failed to induce any changes in the localisation of a-COP:GFP.
The results suggest that microtubules do not function in the transport or positioning of A. nidulans putative Golgi equivalents. Further experiments used a strain expressing a GFPtagged
ER retention signal and an α-COP:GFP-expressing strain to examine the effects
of brefeldin A on the ER and putative Golgi equivalents of A. nidulans.
The α-COP:GFP fusion was introduced into a number of A. nidulans temperature
sensitive mutant strains in an attempt to identify or exclude proteins required for the correct localisation of putative Golgi equivalents. The localisation of α-COP:GFP remained unchanged in a variety of nuclear distribution (nud) mutants up-shifted to the restrictive temperature. The results suggest that the microtubule motor protein dynein and its associated proteins are not required for the transport and positioning of putative Golgi equivalents. The sod^vIC:gfp construct was introduced into a hypA6 mutant background to examine the localisation of putative Golgi equivalents in a strain unable to maintain polar growth. Up-shift experiments caused the illumination of putative Golgi
equivalents within sub-apical cells that later became sites of new growth. The results highlight a key role for Golgi positioning in the initiation of hyphal growth.