The expression of icmW is similar in showing an increase between 0 and 8 hpi, followed by a significant decrease
from 8 to 16 hpi. This was followed by an insignificant change from 16 to 24 hpi. The C. burnetii icmV transcripts increased significantly DNA Damage inhibitor from 0 to 8 and 8 to 16 hpi, followed by a significant decrease from 16 to 24 hpi. However, for dotA, the initial significant increase in expression from 0 to 8 hpi was followed by relatively constant RNA levels. Early expression changes of both dotB and icmT were subtle (Fig. 3). After no significant change in dotB RNA from 0 to 8 hpi, a significant increase from 8 to 16 hpi was followed by a decrease from 16 to 24 hpi, at which time, the dotB RNA, while present, was less than the 0 hpi. The expression of
icmT increased significantly from 0 to 8 hpi, after which little change occurred through 24 hpi. Our analysis indicates that for the icmWicmX and icmTdotB linkage groups, the relative expression of the 3′ gene declines at 24 hpi, while the 5′ gene remains relatively constant. The mechanism for this decrease is not readily apparent in the primary sequence, although partial transcription termination and/or RNase degradation of transcripts could account for the relative decline in the 3′ gene RNA. The icmVdotA linkage group demonstrates a different profile in that the relative amount of RNA for the 3′ gene (dotA) remains elevated at 24 hpi while RNA for the 5′ gene (icmV) declines. This may be a case where an additional EPZ-6438 price promoter of transcription exists for dotA, and this promoter region is activated or increased at 24 hpi while the promoter upstream of icmV decreases. In each of these cases, the differential expression patterns are observed at 24 hpi. This time point during infection is at the end of the lag phase (Coleman et al., 2004) and may indicate that the need for the different T4BSS homologs changes as
C. burnetii transitions into the log growth phase of the infectious cycle. The genome sequence of C. burnetii Nine Mile phase I strain indicated that the bacteria possess three RNA polymerase sigma subunits [rpoD, rpoS, and rpoH, (Seshadri et al., HSP90 2003)]. The rpoS subunit has been shown to be increased in C. burnetii LCVs relative to SCVs (Seshadri & Samuel, 2001), indicating a role in the log growth of the organism. However, a conserved nucleotide sequence-binding site has not been established in C. burnetii (Melnicakova et al., 2003), making searches of the C. bunetii T4BSS RI primary sequence a challenge. In addition, a conserved rpoH binding sequence is poorly defined. Searches of the sequence upstream of each ORF did not reveal any apparent or consensus (rpoD) −10 or −35 binding sequences for the sigma subunits.