# How to model time series with unevenly spaced observations?

I have three time series of the following form:

$$T = T_{2000}, T_{2004}, T_{2008}, …$$

$$U = U_{1998}, U_{1999}, U_{2000}, U_{2001}, U_{2002}, U_{2003}, …$$

$$V = V_{1998}, V_{1999}, V_{2000}, V_{2001}, V_{2002}, V_{2003}, …$$

I would like to predict $$T$$ from $$U + V$$, but since the time series have unequal numbers of observations ($$T$$ has four times less data points: the series 'coincide' only every four years), I am unsure of how to go with it.

Any help (and software recommendations, preferably with R) would be very much appreciated!