Cyclin protein behavior has not been systematically investigated in 
multinucleated cells with asynchronous mitoses. Cyclins are canonical 
oscillating cell cycle proteins, but it is unclear how fluctuating protein 
gradients can be established in multinucleated cells where nuclei in different 
stages of the division cycle share the cytoplasm. Previous work in A. gossypii, 
a filamentous fungus in which nuclei divide asynchronously in a common 
cytoplasm, demonstrated that one G1 and one B-type cyclin do not fluctuate in 
abundance across the division cycle. We have undertaken a comprehensive analysis 
of all G1 and B-type cyclins in A. gossypii to determine whether any of the 
cyclins show periodic abundance across the cell cycle and to examine whether 
cyclins exhibit functional redundancy in such a cellular environment. We 
localized all G1 and B-type cyclins and notably found that only AgClb5/6p varies 
in subcellular localization during the division cycle. AgClb5/6p is lost from 
nuclei at the meta-anaphase transition in a D-box-dependent manner. These data 
demonstrate that efficient nuclear autonomous protein degradation can occur 
within multinucleated cells residing in a common cytoplasm. We have shown that 
three of the five cyclins in A. gossypii are essential genes, indicating that 
there is minimal functional redundancy in this multinucleated system. In 
addition, we have identified a cyclin, AgClb3/4p, that is essential only for 
sporulation. We propose that the cohabitation of different cyclins in nuclei has 
led to enhanced substrate specificity and limited functional redundancy within 
classes of cyclins in multinucleated cells.