Lenses with no internal motor have screwdrives and will work with all Pentax AF bodies. (KAF2 mount)
Some lenses have both an internal motor and the screwdrive. Again, it will work with all Pentax AF bodies. (KAF2 mount)
However, a select few lenses are branded as "SDM-only or DC-only" and have an internal motor, but do not have a screwdrive. They can only autofocus with modern Pentax DSLRs, generally including any body released after the K100D. (KAF3 mount)
A few examples of KAF3 lenses include the Pentax 17-70mm, * 55mm, and 18-135mm. All KAF2 lenses should be able to autofocus on all bodies- so your 55-300 will be kosher with the K-5
Adam
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