Cytidine formed from CMP can
be converted to uridine via cytidine deaminase. An
Arabidopsis cDNA encoding cytidine deaminase (ATCDA1)
was recently cloned andfound to encode polypeptide of 301 amino acids which
had an estimated molecular mass of 32.5 kDa. In contrast,
the molecular mass of recombinant AT-CDA1 estimated by
gel filtration was 63 kDa, indicating that the Arabidopsis
enzyme is a dimer of two identical subunits (Vincenzetti et
al., 1999). The predicted protein lacks transit sequences
for either chloroplasts or mitochondria, suggesting it is
localized in the cytosol. Interestingly uridine has been
reported to be capable of promoting cell division in pea
roots , raising the possibility that CDA
may play a role in nodulation of legume plants .
The absence of cytosine deaminase activity
in plants has led to its development as a negative selectable
marker in several plants including Arabidopsis
.