Spectrum sharing has gained traction in recent years due to the fast reduction of spectrum availability and the growth in the variety of applications that rely on wireless connectivity. This paper presents a novel, database-assisted Medium Access Control (`MAC') protocol that allows an Incumbent operator to share its spectrum with a Licensee operator under agreed rules. To facilitate this, the Incumbent operator shares channel frequency response and measured interference information with the Licensee operator through a shared database. Our simulation results under a `worst case' scenario show that through our approach the Licensee operator manages to use part of available spectrum, while respecting the minimum throughput requirements set by the Incumbent operator. Finally, we discuss on the effect of directional antennas which can further increase the performance gains, proving that spectrum sharing is a viable proposition.