cDNA Library Screening Protocol - lZAPII

 

Procedure:

 

1) Streak XLI-Blue MRFÕ (#1059; in Box 1A of Locator) from frozen stock on an LB-tetracycline plate.  Incubate plate overnight at 37¡C.  Pour NZY plates and store at room temp. to dry out.  May need to place at 37¡C for 2 hr with lid slightly ajar to complete drying. 

 

 2) Pick a single XLI-Blue MRFÕ colony with a sterile toothpick to inoculate 50 ml of LB broth containing 0.5 ml of 20% maltose and 0.5 ml of 1M MgSO4 in a sterile 250 ml flask.  Grow overnight at 30¡C (Green lab water bath).

 

3) Spin for 10 min at 2000 rpm in a sterile 50 ml conical using Beckman GS 6R centrifuge.  Carefully decant media and gently resuspend pellet in 15 ml of 10 mM MgSO4 (donÕt vortex).  Dilute cells to OD600 = 0.5 with 10 mM MgSO4.  Will need 0.6 ml of diluted cells per 150 mm NZY plate.  Store diluted cells at 4¡C (use within 2 - 3 days).

 

4)  To titer phage library, thaw phage, and aliquot if it is a newly received library.  Newborn mouse brain lZAPII library is #1055 in white box#11 of -70¡C freezer.  Add 3 µl of 10 fold dilutions of phage (undil. to 1/2000; dilute in 10 mM MgSO4; best dilution for #1055 in Exp.1727 was 1/1000 - 1/1333) to 600 µl of diluted cells (from step 3)) in sterile blue top (#14-956-4A) tubes.  Mix by shaking or gently vortexing, then incubate for 15 min at 37¡C on a shaker.  During this time, melt top agarose and have cooling to 47¡C (check temperature on outside of bottle with BioRad temp. indicator strip).

 

5) Add 6.5 ml of 47¡C top agarose (keep top agarose in a 50¡C water bath on the bench by the flame to keep from solidifying) to the first tube, mix by inversion several times, then quickly pour onto the center of a 150 mm NZY plate.  Quickly swirl to promote even distribution. Repeat with the next tubes.  After all plates have been poured and hardened, invert and incubate at 37¡C.  Count # of plaques after 12-16 hrs. 

 

6) Using same host cells from 3), dilute phage to give 15,000 - 20,000 cfu/150 mm plate.  Do 20 plates, as per 4) and 5).  Incubate 12-16 hrs at 37¡C.

 

7) Put plates at 4¡C for 2 hrs.  During this time, prepare solutions to be used in steps 7) - 9), including prehybridization and hybridization solutions which should be placed in a 42¡C incubator to warm.  Label first 137 mm filter (Stratagene #420107) with fine tip indelible marker to correspond to plate.  Holding filter at edge with blunt ended forceps, place filter onto plaque surface.  Mark filter in 3 asymmetric locations by stabbing through it and agar with 18 gauge needle attached to a syringe containing waterproof black ink.  After 1 min, pull off filter and immerse DNA side up for 1-5 min in a glass tray containing 500 ml of 0.5 N NaOH, 1.5 M NaCl (25 ml of 10 N NaOH and 150 ml of 5 M NaCl made up to 500 ml in ddH2O).  After 10 filters, will need replace this with fresh denaturing solution.

 

8) Remove and transfer to neutralizing solution for 5 min consisting of 500 ml of 1.5 M NaCl, 0.5 M Tris, pH 7.4 (150 ml of 5 M NaCl and 250 ml of 1 M Tris, pH 7.4 made up to 500 ml in ddH2O).

 

9) Rinse filter in two successive 2 x SSC baths (400 ml each; 80 ml of 20 x SSC made up to 800 ml in ddH2O), then place DNA side up on fresh 3MM  Whatman or bench top paper to dry (1 hr).  When all filters are dry, sandwich each between 3MM Whatman paper, and bake at 80¡C for 2 hrs under vacuum (need dry ice in trap). 

 

10) Allow filters to cool, then individually wet in 2 x SSC (in a 150 mm petri dish; need about 50 ml), followed by immersion in prewarmed prehybridization solution contained also in a 150 mm petri dish supported in a plastic box.  Put top on box, and put in incubator at 42¡C for 4 hrs with gentle swirling. 

 

11) During prehybridization, label cDNA probe (purified insert) by random priming method (Pharmacia #27-9251-01).  Reconstitute reaction mix by adding 20 µl of ddH2O and place on ice for 5-60 min.  Make 1.8 µl of insert up in 25 µl of TE, pH 8 and denature for 3 min at 95¡C.  Cool on ice for 2 min, then add diluted/denatured insert to reaction mix.  Behind lucite, add 5 µl of 32PdCTP (ICN #33004X).  Carefully mix by pipetting up and down.  Incubate at 37¡C for 15-30 min.  Purify probe using a Nick Spin Column (Pharmacia #17-0862-02) or equivalent (Qiagen #28304) and check cpmÕs in Scintillation counter.  Denature probe (3 min at 95¡C, on ice for 2 min) prior to addition to hybridization solution.  After prehyb, individually transfer filters into a 150 mm petri dish (in plastic box) containing hybridization solution.  Place top on box and put in incubator at 42¡C overnight with gentle swirling.

 

         Prehybridization SolÕn                     Hybridization SolÕn

                  ddH2O         15.3 ml                                  ddH2O         15.3 ml

         Formamide           15 ml                   Formamide           15 ml

         20 x SSPE            12.5 ml                         20 x SSPE            12.5 ml

         20% SDS              0.25 ml                         20% SDS              0.25 ml

         50 x DenhardtÕs   5 ml                              50 x DenhardtÕs   5 ml

         Salmon Sp. DNA   2 ml                              Salmon Sp. DNA   2 ml

         Poly A                  5 µl                              Poly A                  5 µl

                                                                        32cDNA probe       50-100 µl

 

(note: Salmon Sperm DNA stock is 5 mg/ml; Poly A stock is 10 mg/ml; make up prehyb and hyb solÕns in 50 ml conicals)

        

12) Remove filters individually into 400 ml of room temperature 2 x SSC, 0.1% SDS (80 ml of 20 x SSC and 4 ml of 20% SDS made up to 800 ml in ddH2O).  Wash for 5 min on rotator.  Do two additional washes.  Transfer filters to 400 ml of prewarmed (42 - 65¡C; use 42¡C for wheat-mouse and 65¡C for mouse-mouse hybridizations) 0.1 x SSC, 0.1% SDS (4 ml of 20 x SSC and 4 ml of 20% SDS made up to 800 ml in ddH2O).  Wash for 20 min on rotator.  Do a total of three 20 min washes.  

 

13) Allow filters to dry on fresh bench paper, then place on Whatman 3MM paper in a large x-ray cassette holder.  Cover with plastic wrap.  Under red light in the dark room, place x-ray film on, followed by an enhancing screen.  Close up and expose overnight at -70¡C.  The next day develop film.  Copy location of positive plaques and three asymmetric ink marks onto a clear acetate sheet. Place acetate sheet on bottom of original 150 mm plate and identify positive plaques.

 

14) Pick positive plaques by stabbing with a plastic transfer pipet, and squirt into 1 ml of SM containing a drop of chloroform.  Let sit for 1-2 hrs at RT or overnight at 4¡C.  Vortex gently.  Dilute 1/100 (2 µl up to 200 µl) in 10 mM MgSO4.  Add 50 µl of diluted sample with 600 µl of XLI-Blue MRFÕ host cells (OD600=0.5), and mix, then incubate for 15 min at 37¡C on a shaker.  Add 6.5 ml of 47¡C top agarose, mix by inversion several times, then quickly pour onto the center of a 150 mm NZY plate.  Quickly swirl to promote even distribution.  Incubate at 37¡C.  Repeat steps 7) - 13).  This is the 2¡ screen.

 

15)  For the tertiary screen, pick positive plaques, as in 14).  Dilute 1/1500 so that plaques will be well separated.  Mix with host cells as above and plate with top agarose.  Repeat steps 7) - 13).  All plaques should now be positive.  Pick a well-separated plaque from each of the tertiary screen clones.  Place in 500 µl of SM containing 20 µl of chloroform, vortex gently and incubate for 2 hr at RT, or store at 4¡C.  Go to ÔExcision of Clones as pBluescript from lZAPIIÕ.  NOTE: to do excision experiment on same day as tertiary plaque picking, need to have prepared overnight cultures of XLI Blue MRFÕ and SOLR (established from fresh streaked plates).