381 Bulletin UASVM Animal Science and Biotechnologies, 67(1-2)/2010 Print ISSN 1843-5262; Electronic ISSN 1843-536X High-Frequency of P{lacW} Double Local Reinsertions in Chromosomal Region 100C of Drosophila melanogaster are Amenable to a Homing-Like Mechanism Alexandru Al. ECOVOIU 1)* , Attila C. RATIU 1)* , Marian GRAUR 1) , Lorand SAVU 2) 1) University of Bucharest, Department of Genetics, 1-3 Portocalelor Alley, 060101 Bucharest, Romania; ratiuattila@botanic.unibuc.ro 2) Genetic Lab, 43B Ghencea Bv., Bucharest, Romania Abstract. Herein we present results concerning the transposition pattern of the P{lacW} artificial mobile element in the male germline of Drosophila melanogaster. Using the power of inverse PCR followed by sequencing strategy to analyze a collection of 55 transgenic lines, we recovered 18 independent secondary reinsertions of the P{lacW} gammaCop057302 parental transposon affecting gammaCop gene located in 100C. Bioinformatics investigation revealed that 8 out of them reside within or very close to the starting element, representing extreme cases of secondary local reinsertions (equivalent to double local reinsertions). Similar molecular phenomena were previously reported for a PZ artificial element transposing in the male germline. Mapping of some secondary reinsertions obtained in our experiment revealed two putative insertional hot-spots located in the 3' half of P{lacW}, namely in the mini-white allele and in the adjacent pBR322 fragment. The relative high frequency of double local reinsertions resemble homing, a phenomenon consisting in the preferential insertion of transgenic transposons harboring fragments from a D. melanogaster gene into or nearby the genomic copy of the cloned gene. Such biases in the pattern of transposition of artificial mobile elements may be products of a molecular behavior with still unknown biological significance. Keywords: P{lacW} transposition, inverse PCR, secondary local reinsertion, homing, gammaCop gene INTRODUCTION P elements derivatives, such as P{lacW} artificial transposon (Bier et al., 1989), are among the most important genetic tools available in D. melanogaster. In order to search for a biological significance of P elements transposition patterns we artificially induced the mobilization of P{lacW} gammaCop057302 artificial transposon, uniquely inserted in 5'UTR of gammaCop gene, which localizes in 100C chromosomal region (Ecovoiu et al., 2002a; Ecovoiu et al., 2002b). For the analysis of the phenomena derived from the mobilization we defined a couple of terms. The primary local reinsertion (PLR) refer to the reintroduction of a copy of the original transposon at the initial donor site and secondary local reinsertion (SLR) was used to describe the reinsertion of the excised transposon within the same chromosome (Ecovoiu et al., 2009; Ratiu et al., 2008). Insertional mutagenesis have been previously used in order to decipher the pattern of P elements transposition (Tower et al., 1993; Zhang and Spradling, 1993), but the methods for analyzing the data were laborious and time consuming. In this study we used for the analysis of the new insertional lines an experimental strategy employing inverse PCR followed by