Primase

 Primase is a RNA polymerase which is responsibe for the synthesis for a short peice of RNA which is then able to act as a primer in DNA synthesis. The synthesised RNA primer is very small in size (approximately 5 nucleotides long) and synthesis of the primer can be iniated without the presence of another primer. The primer is complementary to a section of DNA and hence binds to it, thus allowing DNA polymerase III to iniate synthesis of new DNA in the 5' to 3' direction. At a later stage of DNA synthesis the primer is removed and replaced by DNA (for example this is done on the lagging starnd of DNA by DNA polymerase I which contins an exonucleas enzyme).

References: 

Berg J.M., Tymoczko J.L., Styer L. (2012) Biochemistry, 7th edition, New York, W.H Freeman.