HETEROCYST - Cyanobacteria - page 198

genes. In this category are included genes that are required in the synthesis and transport of Hgls and
envelope polysaccharides, which are deposited one after another in the form of a laminated layer
and heterocyst envelope, respectively at the time of maturation of heterocyst. The characterization
of a Tn5-1063 insertion mutant, M7 (Fox - , Het + and Hen - ) revealed that it is defi cient in aerobic
nitrogen fi xation though differentiates heterocysts that are devoid of both normal polysaccharide
layer and heterocyst-specifi c glycolipids (Ernst et al ., 1992). Maldener et al . (1994) recovered the Tn5-
inserted chromosomal segment from M7 and found that due to its insertion a 732-bp ORF has been
inactivated. This has been designated by them as devA (for development). Wild-type Anabaena sp.
strain PCC 7120 subjected to directed mutagenesis of devA gene also yielded a mutant phenotype that
resembled M7. The wild-type gene sequence of devA on a shuttle vector could also complement the M7
mutant. Sequencing of devA and the deduced amino acid sequence of DevA protein (244 amino acids)
showed it to be a component of a periplasmic permease required for heterocyst maturation. DevA
protein showed a strong similarity to ATP-binding subunit of the traffi c ATPases. Two additional
genes, devC and devB are present upstream of devA , and constitute a devBCA operon (Fiedler et al .,
1998). devC (earlier designated by Maldener et al ., 1994 as OrfA ) occurs 1800 bp upstream of devA
and is 1154 bp long that encodes a membrane-spanning protein (of 384 amino acids long) of ABC
transporters. devB is 1425 bp long and present upstream of devC separated by 41 bp that encodes a
membrane fusion protein (of 474 amino acids length) of ABC exporters. Although M7 synthesizes
heterocyst-specifi c glycolipids, these are not transported to the envelope to form the laminated

Table 2: Development genes expressed at late stages of heterocyst differentiation in Anabaena sp. strain PCC 7120.

Gene Gene product and time

of appearance

Role Mutant

phenotype

Reference(s)

devBCA operon
(dev for
development)
devB ( alr3710 )
1425 bp long

Membrane fusion protein of 474
amino acids long; 12 to 14 h of N
step-down

Heterocyst maturation Fox - , Het + ,

Hen -

Fiedler et al . (1998)

devC *
( alr3711 )
1154 bp long

Membrane spanning protein of
ABC transporters of 384 amino
acids long; 12 to 14 h of N step-
down

Heterocyst maturation Fox - , Het + ,

Hen -

Fiedler et al . (1998)

devA
( alr3712 )
732 bp long

Periplasmic permease of 244
amino acids long; 12-14 h of N
step-down

Heterocyst maturation Fox - , Het + ,

Hen -

Maldener et al .
(1994)

devH
( alr3592 )

DNA binding protein/
transcriptional regulator; 29
kDa protein bears resemblance
to cAMP receptor protein and
nitrogen regulator NtcA; at 24 h
a major transcript of 1.0 kb and
a minor transcript of 1.25 kb
appear at 48 h after N step-down

Regulates expression of
hgl genes hglC , hglE1 , hglB ,
hglD and hglE2

Fox - , defective
in the formation
of Hgls

Hebbar and Curtis
(2000),
Ramirez et al .
(2005)

devR **
( alr0442 )
405 bp long

Receiver domain of response
regulator of 135 amino acids long

Responsible for a sensory
pathway that is not
responsive to cellular N
status

Fox - Zhu et al . (1998),

Zhou and Wolk
(2003)

*The former gene designation of devC was OrfA described by Maldenet et al . (1994).
** devR was initially described by Campbell et al . (1996) in N. punctiforme ATCC 29133.