  The formation of Wolf-Rayet central stars of planetary nebulae ([WR] CSPNe)
whose spectroscopic appearance mimics massive WR stars remains poorly
understood. Least understood is the nature and frequency of binary companions
to [WR] CSPNe that may explain their H-deficiency. We have conducted a
systematic radial velocity (RV) study of 6 [WR] CSPNe to search for
post-common-envelope (post-CE) [WR] binaries. We used a cross-correlation
method to construct the RV time-series as successfully done for massive close
binary WR stars. No significant RV variability was detected for the late-[WC]
type nuclei of Hen 2-113, Hen 3-1333, PMR 2 and Hen 2-99. Significant,
large-amplitude variability was found in the [WC4] nucleus of NGC 5315. In the
[WO1] nucleus of NGC 5189 we discovered significant periodic variability that
reveals a close binary with $P_\mathrm{orb}=4.04\pm0.1$ d. We measured a
semi-amplitude of $62.3\pm1.3$ km s$^{-1}$ that gives a companion mass of
$m_2\ge0.5$ $M_\odot$ or $m_2=0.84$ $M_\odot$ (assuming $i=45^\circ$). The most
plausible companion type is a massive WD as found in Fleming 1. The spectacular
nebular morphology of NGC 5189 fits the pattern of recently discovered post-CE
PNe extremely well with its dominant low-ionisation structures (e.g. as in NGC
6326) and collimated outflows (e.g. as in Fleming 1). The anomalously long 4.04
d orbital period is either a once-off (e.g. NGC 2346) or it may indicate there
is a sizeable population of [WR] binaries with massive WD companions in
relatively wide orbits, perhaps influenced by interactions with the strong [WR]
wind.
