  We present preliminary results concerning the search for short-period
variable stars in Tucana and LGS3 based on very deep HST/ACS imaging. In the
fraction of the observed field we studied in each galaxy, a total of 133 and 30
variables were found, respectively. For Tucana, we identified 76 of them as RR
Lyrae (RRL) stars pulsating in the fundamental mode (RRab) and 32 in the
first-overtone mode (RRc), as well as 2 anomalous Cepheids (AC). The mean
period of the RRab and RRc is 0.59 and 0.35 days, respectively. In the case of
LGS3, we found 24 RRab and 4 RRc, with mean periods 0.61and 0.39 days,
respectively, plus two candidate ACs. These values place both galaxies in the
Oosterhoff gap.
